Datasheet AM79C976KCWV, AM79C976KIW Datasheet (AMD Advanced Micro Devices)

Page 1

PRELIMINARY

This document contains information on a product under development at Advanced Micro Devices. The information is intended to help you ev aluate this produc t. AMD reserves the right to chang e or discontinu e work on this proposed product without notice.

Publication# 22929 Rev: C Amendment/0 Issue Date: August 2000

Refer to AMD’s Website (www.amd.com) for the latest information.



Am79C976

PCnet-PRO™ 10/100 Mbps PCI Ethernet Controller

DISTINCTIVE CHARACTERISTICS

■ Integrated Fast Ethernet controller for the

Peripheral Component Interconnect (PCI) bus — 32-bit gluele ss PCI hos t interf ace — Supports PCI clock frequency from DC to

33 MHz independent of network clock

— Supports network operation with PCI clock

from 15 MHz to 33 MHz

— High performance bus mastering

architecture with integrated Direct Memory Access (DMA) Buffer Management Unit for low CPU and bus utilization

— PCI specification revision 2.2 compliant — Supports PCI Subsystem/Subvendor

ID/Vendor ID programming through the EEPROM interface

— Supports both PCI 3.3-V and 5.0-V signaling

environments

— Plug and Play compatible — Uses advanced PCI commands (MWI, MRL,

MRM)

— Optionally supports PCI bursts aligned to

cache line boundaries

— Supports big endian and little endian byte

alignments

— Implements optional PCI power management

event (PME

) pin

— Supports 40-bit addressing (using PCI Dual

Address Cycles)

■ Media Independent Interface (MII) for

connecting external 10/100 megabit per second (Mbps) transceivers

— IEEE 802.3-compliant MII — Intelligent Auto-Poll™ external PHY status

monitor and interrupt

— Supports both auto-negotiable and non auto-

negotiable external PHYs

— Supports 10BASE-T, 100BASE-TX/FX,

100BASE-T4, and 100BASE-T2 IEEE 802.3compliant MII PHYs at full- or half-duplex

■ Full-duplex operation supported with

independent Transmit (TX) and Receive (RX) channels

■ Includes support for IEEE 802.1Q VLANs

— Automatically inserts, deletes, or modifies

VLAN tag

— Optionally filters untagged frames

■ Provides optional flow control features

— Recognizes and transmits IEEE 802.3x MAC

flow control frames

— Asserts collision-based back pressure in

half-duplex mode

■ Provides internal Management Information

Base (MIB) counters for network statistics

■ Supports PC97, PC98, PC99, and Net PC

requirements — Implements full OnNow features including

pattern matching and link status wake-up

— Implements Magic Packet™ mode — Magic Packet mode and the physical address

loaded from EEPROM at power up without requiring PCI clock

— Supports PCI Bus Power Management

Interface Specification Version 1.1

— Supports Advanced Configuration and

Power Interface (ACPI) Specification Version

1.0

— Supports Network Device Class Power

Management Specification Version 1.0

■ Large independent external TX and RX FIFOs

— Supports up to 4 megabytes (Mbytes)

external SSRAM for RX and TX frame storage

— Programmable FIFO watermarks for both

transmit and receive operations

— Receive frame queuing for high latency PCI

bus host operation

— Programmable allocation of buffer space

between transmit and receive queues

Page 2

2 Am79C976 8/01/00

PRELIMINARY

■ Dual-speed CSMA/CD (10 Mbps and 100 Mbps)

Media Access Controller (MAC) compliant with IEEE/ANSI 802.3 and Blue Book Ethernet standards

■ Programmable internal/external loopback

capabilities

■ Supports patented External Address Detection

Interface (EADI) with receive frame tagging support for internetworking applications

■ EEPROM interface supports jumperless design

and provides through-chip programming — Supports full programmability of all internal

registers through EEPROM mapping

■ Programmable PHY reset output pin capab le of

resetting external PHY without needing buffering

■ Integrated oscillator circuit is controlled by

external crystal

■ Extensive programmable LED status support

■ Supports up to 16 Mbyte optional Boot PR OM or

Flash for diskless node application

■ Look-Ahead Packet Processing (LAPP) data

handling technique reduces system overhead by allowing protocol analysis to begin before the end of a receive frame

■ Optional delayed interrupt feature reduces CPU

overhead

■ Programmable Inter Packet Gap (IPG) to

address less aggressive network MAC controllers

■ Offers the Modified Back-Off algorithm to

address the Ethernet Capture Effect

■ Optionally sends and receives non-standard

frames of up to 64K octets in length

■ IEEE 1149.1-compliant JTAG Boundary Scan

test access port interface for board-level production connectivity test

■ Provides built-in self test (MBIST) for the

external SSRAM

■ Software compatible with AMD PCnet Family

and LANCE/C-LANCE register and descriptor architecture

■ Compatible with the existing PCnet Family

driver and diagnostic software (except for statistics)

■ Available in 208-pin PQFP package

■ +3.3-V power supply with 5-V tolerant I/Os

enables broad system compatibility

■ Support for operation in Industrial temperature

range (-40° C to +85

 C) available.

Page 3

8/01/00 Am79C976 3

PRELIMINARY

GENERAL DESCRIPTION

The Am79C976 controll er is a highly-integrated 32- bit full-duplex, 10/100-Megabit per second (Mbp s) Ethernet controller solution, designed to address highperformance system application requirements. It is a flexible bus mastering device that ca n be used in any application, including network-ready PCs and bridge/ router designs. The bus master architecture provides high data throughput and low CPU and system bus utilization. The Am79C976 controller is fabricated with advanced low-power 3.3-V CMOS p rocess to provid e low operating current for power sensitive applications.

The Am79C976 controller also has several enhancements over its predecessor, the Am79C971 PCnet-FAST d evice. In addi tion t o providing acc ess t o a larger SSRAM, it fur ther reduces s ystem implementation cost by the addition of a new EEPROM programmable pin (PHY_RST) and the integration of the PAL function needed for Magic Packet application. The PHY_RST pin is i mplemented to reset the external PHY without increasing the load to the PCI bus and t o block RST

to the PHY when PG input is LOW.

The 32-bit multiplexed bus interface unit provides a d irect interface to the P CI local bus, simplif ying the design of an Ethernet node in a PC system. The Am79C976 contr oller provides the complet e interface to an Expansion ROM or Flash device allowing add-on card designs with onl y a single lo ad per PCI bus interface pin. With its built-in suppor t for both little and big endian byte alignment, this controller also addresses non-PC applications. The A m79C976 controller’s advanced CMOS design allows the bus interface to be connected to eithe r a +5-V o r a +3.3-V signalin g environment. An IEEE 1149.1-compliant JTAG test interface for board-level testing is also provided.

The Am79C976 controller is also compliant with the PC97, PC98, PC99, and Network PC (Net PC) specifications. It includes the full implementation of the Microsoft OnNow and ACPI specifications, which are backward compatible with the Magic Packet technology, and it is compliant with the PCI Bus Power Management Interface Specifica tio n by sup porting the four power management states ( D0, D1, D2, and D3), th e optional PME

pin, and the necessary configuration and

data registers. The Am79C976 control ler is ideal ly suited for Net PC,

motherboard, net work interface card (N IC), and embedded designs. It is available in a 208-pin Plastic Quad Flat Pack (PQFP) package.

The Am79C976 controller contains a bus interface unit, a DMA Buffer Management Unit, an ISO/IEC 8802-3 (IEEE 802.3)-compliant Media Access Controller (MAC), and an IEEE 802.3-compliant MII. An i nter face to an external RAM of up to 4 Mbytes is provided for frame storage. The MII supports IEEE 802.3-compliant full-duplex and half-duplex operations at 10 Mbps or 100 Mbps. The MII TX an d RX clock signals can be stopped independently for home networking applications.

The Am79C976 controller is register compatible with the LANCE™ (Am7990) and C-LANCE™ (Am79C 90) Ethernet controllers, and all Et hernet contro ll ers in the PCnet Family except ILACC™ (Am79C900), including the PCnet™-ISA controller (Am79C960), PCnet™-ISA+ (Am79C961), PCnet™-ISA II (Am79C961A), P Cnet™-32 (Am79C965) , PCnet™PCI (Am79C970), PCn et™-PCI II (Am79C970A), and the PCnet™-FAST (Am79C971).

The Buffer Management Unit supports the LANCE and PCnet descriptor software models.

The Am79C976 controll er suppor ts auto- configuration in the PCI configu ration space. Additional Am79C976 controller configuration parameters, including the unique IEEE physical address, can be read from an external nonvolatile memory (EEPROM) immediately following system reset.

In addition, the device provides programmable on-chip LED drivers f or tr ansmit, re ceiv e, coll ision, lin k integrity, Magic Packet status, activit y, addre ss match, fullduplex, or 100 Mbps status. The Am79C976 controller also provides an EADI to al low external hardware address filtering in interne tworking applications and a receive frame tagging feature.

With the rise of embedded networking applications operating in harsh environments where temperatures may exceed the normal commercial temperature (0

 C

to +70

 C) window, an industrial temperature (-40 C to

+85

 C) version is available. This industrial temperature

version of the PCnet-PRO Ethernet co ntroller is characterized across the industrial temperature range (-40



C to +85 C) within the published power supply specification (4.75V to 5.25V;

±5% Vcc). Thus, conformance

of the PCnet-PRO performance over this temperature range is guaranteed by a design and character i zatio n monitor.

Page 4

4 Am79C976 8/01/00

PRELIMINARY

BLOCK DIAGRAM

CLK

RST

AD[31:0]

C/BE[3:0]

PAR

FRAME

TRDY

IRDY

STOP

IDSEL

DEVSEL

REQ

GNT PERR SERR

INTA

PCI Bus

Interface

Unit

93CXX

EEPROM

Interface

Expansion Bus

Interface

MIB

Counters

JTAG

Port

Control

OnNow

Power

Management

Unit

802.3 MAC Core

MII

Port

EADI

Port

ERADV/FLOE ERADSP/ICEN ERCLK ERD[31:0]/FLD[7:0]/FLA[23.20] ERA[19:0]/FLA[19:0] ERCE EROE ERWE FLCS

PME

RWU

WUMI

PHY_RST

TXD[3:0] TX_EN TX_CLK COL RXD[3:0] RX_ER RX_CLK RX_DV CRS

SFBD EAR RXFRTGD RXFRTGE

EECS EESK

EEDI

EEDO

LED0 LED1 LED2 LED3

Network Port

Manager

MDC MDIO

Memory Control

Unit

and Status Unit

Descriptor

Management Unit

LED

Control

VAUX_SENSE

Clock

Generator

XTAL1 XTAL2 XCLK CLKSEL0 CLKSEL1 CLKSEL2

TCK

TMS

TDI

TDO

TEST

22929B1

Page 5

8/01/00 Am79C976 5

PRELIMINARY

DISTINCTIVE CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

BLOCK DIAGRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

TABLE OF CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

LIST OF FIGURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

ORDERING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Standard Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

CONNECTION DIAGRAM (PQR208) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

PIN DESIGNATIONS (PQR208) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Listed By Pin Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Listed By Group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

PIN DESCRIPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

PCI Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Board Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

EEPROM Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

External Memory Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Media Independent Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

External Address Detection Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

IEEE 1149.1 (1990) Test Access Port Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Power Supply Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

BASIC FUNCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

System Bus Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Software Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Network Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

DETAILED FUNCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Slave Bus Interface Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Slave Configuration Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Slave I/O Transfers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Expansion ROM Transfers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Slave Cycle Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Disconnect When Busy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Disconnect Of Burst T ransfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Parity Error Response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

Master Bus Interface Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Bus Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Bus Master DMA Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Basic Non-Burst Read Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Basic Burst Read Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

Basic Non-Burst Write Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Basic Burst Write Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

DMA Burst Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

Target Initiated Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Disconnect With Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

Disconnect Without Data Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

Target Abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

Master Initiated Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Preemption During Non-Burst Transaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

Preemption During Burst Transaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

Master Abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

Parity Error Response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

Initialization Block DMA Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

Descriptor DMA Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

FIFO DMA Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

Descriptor Management Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

TABLE OF CONTENTS

Page 6

6 Am79C976 8/01/00

PRELIMINARY

Re-Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Run and Suspend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Descriptor Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Descriptor Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Polling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

Transmit Polling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Receive Polling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

Look Ahead Packet Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Software Interrupt Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66

Media Access Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Transmit and Receive Message Data Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Framing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Destination Address Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

Error Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Media Access Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

Medium Allocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Signal Quality Error (SQE) Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

Collision Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

Transmit Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Transmit Function Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Automatic Pad Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Transmit FCS Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Transmit Error Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

Loss of Carrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Late Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Transmit FIFO Underflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

Receive Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

Receive Function Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

Address Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

Automatic Pad Stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72

Receive FCS Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Receive Exception Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

Statistics Counters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Receive Statistics Counters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

Transmit Statistics Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

VLAN Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

VLAN Frame Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Admit Only VLAN Frames Option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

VLAN Tags in Descriptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Loopback Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Miscellaneous Loopback Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80

Full-Duplex Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Full-Duplex Link Status LED Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

Media Independent Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

MII Transmit Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

MII Receive Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

MII Network Status Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

MII Management Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

MII Management Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

Host CPU Access to External PHY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Auto-Poll State Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

Network Port Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

Auto-Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Auto-Negotiation With Multiple PHY Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Operation Without MMI Management Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

Regulating Network Traffic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

MAC Control Pause Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

Back Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

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Enabling Traffic Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

Hardware Control of Traffic Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

Software Control of Traffic Regulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

Programming the Pause Length Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89

PAUSE Frame Reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89

Delayed Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

External Address Detection Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

External Address Detection Interface: Receive Frame Tagging . . . . . . . . . . . . . . . . . . . . . . . . . .91

External Memory Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Expansion ROM - Boot Device Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92

Direct Flash Access. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

Flash/EPROM Read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

SRAM Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

EEPROM Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Automatic EEPROM Read Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

EEPROM Auto-Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Direct Access to the Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

EEPROM CRC Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

LED Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

Power Savings Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

Power Management Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

OnNow Wake-Up Sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

RWU Wake-Up Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

Link Change Detect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

Magic Packet Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

OnNow Pattern Match Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

Pattern Match RAM (PMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

IEEE 1149.1 (1990) Test Access Port Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

Boundary Scan Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

TAP Finite State Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Supported Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Boundary Scan Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

Other Data Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

H_RESET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

EE_RESET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

S_RESET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

STOP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

Power on Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

External PHY Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

Software Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

PCI Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

I/O Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

I/O Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Address PROM Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Reset Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

Word I/O Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Double Word I/O Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108

USER ACCESSIBLE REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

PCI Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

PCI Vendor ID Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

PCI Device ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

PCI Command Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

PCI Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113

PCI Revision ID Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

PCI Programming Interface Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

PCI Sub-Class Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

PCI Base-Class Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

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PCI Cache Line Size Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

PCI Latency Timer Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

PCI Header Type Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

PCI I/O Base Address Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

PCI Memory Mapped I/O Base Address Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116

PCI Subsystem Vendor ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116

PCI Subsystem ID Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

PCI Expansion ROM Base Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

PCI Capabilities Pointer Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

PCI Interrupt Line Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

PCI Interrupt Pin Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

PCI MIN_GNT Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

PCI MAX_LAT Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

PCI Capability Identifier Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

PCI Next Item Pointer Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

PCI Power Management Capabilities Register (PMC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

PCI Power Management Control/Status Register (PMCSR). . . . . . . . . . . . . . . . . . . . . . . . . . . .120

PCI PMCSR Bridge Support Extensions Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121

PCI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121

Memory-Mapped Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

MIB Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122

AP_VALUE0: Auto-Poll Value0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122

AP_VALUE1: Auto-Poll Value1 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122

AP_VALUE2: Auto-Poll Value2 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123

AP_VALUE3: Auto-Poll Value3 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123

AP_VALUE4: Auto-Poll Value4 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123

AP_VALUE5: Auto-Poll Value5 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123

AUTOPOLL0: Auto-Poll0 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

AUTOPOLL1: Auto-Poll1 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

AUTOPOLL2: Auto-Poll2 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

AUTOPOLL3: Auto-Poll3 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

AUTOPOLL4: Auto-Poll4 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

AUTOPOLL5: Auto-Poll5 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

BADR: Receive Ring Base Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128

BADX: Transmit Ring Base Address Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129

CHIPID: Chip ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129

CHPOLLTIME: Chain Poll Timer Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129

CMD0: Command0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130

CMD2: Command2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131

CMD3: Command3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135

CMD7: Command7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138

CTRL0: Control0 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139

CTRL1: Control1 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140

CTRL2: Control2 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143

CTRL3: Control3 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144

DATAMBIST: Memory Built-in Self-Test Access Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145

DELAYED_INT: Delayed Interrupts Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147

EEPROM_ACC: EEPROM Access Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

FLASH_ADDR: Flash Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

FLASH_DATA: Flash Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150

FLOW: Flow Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151

IFS1: Inter-Frame Spacing Part 1 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152

INT0: Interrupt0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

INTEN0: Interrupt0 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155

IPG: Inter-Packet Gap Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157

LADRF: Logical Address Filter Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157

LED0 Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158

LED1 Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159

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LED2 Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159

LED3 Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159

MAX_LAT_A: PCI Maximum Latency Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160

MIN_GNT_A: PCI Minimum Grant Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160

PADR: Physical Address Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160

Pause Count Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

PCIDATA0: PCI DATA Register Zero Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161

PCIDATA1: PCI DATA Register One Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161

PCIDATA2: PCI DATA Register Two Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162

PCIDATA3: PCI DATA Register Three Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162

PCIDATA4: PCI DATA Register Four Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

PCIDATA5: PCI DATA Register Five Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

PCIDATA6: PCI DATA Register Six Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162

PCIDATA7: PCI DATA Register Seven Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

PHY Access Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163

PMAT0: OnNow Pattern Register 0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164

PMAT1: OnNow Pattern Register 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164

PMC_A: PCI Power Management Capabilities Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Receive Protect Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165

RCV_RING_LEN: Receive Ring Length Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

ROM_CFG: ROM Base Address Configuration Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166

SID_A: PCI Subsystem ID Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166

SRAM Boundary Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167

SRAM Size Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167

STAT0: Status0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168

Software Timer Value Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169

SVID_A: PCI Subsystem Vendor ID Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

VID_A: PCI Vendor ID Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

XMT_RING_LEN: Transmit Ring Length Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

XMTPOLLTIME: Transmit Poll Timer Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

RAP Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

RAP: Register Address Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172

Control and Status Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

CSR0: Am79C976 Controller Status and Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

CSR1: Initialization Block Address 0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

CSR2: Initialization Block Address 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

CSR3: Interrupt Masks and Deferral Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

CSR4: Test and Features Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177

CSR5: Extended Control and Interrupt 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179

CSR6: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181

CSR7: Extended Control and Interrupt 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181

CSR8: Logical Address Filter 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

CSR9: Logical Address Filter 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

CSR10: Logical Address Filter 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

CSR11: Logical Address Filter 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

CSR12: Physical Address Register 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

CSR13: Physical Address Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185

CSR14: Physical Address Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185

CSR15: Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185

CSR16-23: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .186

CSR24: Base Address of Receive Ring Lower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187

CSR25: Base Address of Receive Ring Upper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187

CSR26-29: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187

CSR30: Base Address of Transmit Ring Lower. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187

CSR31: Base Address of Transmit Ring Upper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187

CSR32-46: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188

CSR47: Transmit Polling Interval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188

CSR48: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188

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CSR49: Chain Polling Interval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188

CSR50-57: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189

CSR58: Software Style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189

CSR59-75: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191

CSR76: Receive Ring Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191

CSR77: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191

CSR78: Transmit Ring Length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191

CSR79: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191

CSR80: DMA Transfer Counter and FIFO Threshold Control . . . . . . . . . . . . . . . . . . . . . . . . . . .191

CSR81-87: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR88: Chip ID Register Lower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR89: Chip ID Register Upper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR90-99: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR100: Bus Timeout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR101-111: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

CSR112: Missed Frame Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR113: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR114: Receive Collision Count. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR115: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

CSR116: OnNow Power Mode Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194

CSR117-121: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

CSR122: Advanced Feature Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195

CSR123: Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195

CSR124: Test Register 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

CSR125: MAC Enhanced Configuration Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .196

Bus Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

BCR0: Master Mode Read Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .198

BCR1: Master Mode Write Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .198

BCR2: Miscellaneous Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

BCR4: LED0 Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

BCR5: LED1 Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201

BCR6: LED2 Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .203

BCR7: LED3 Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205

BCR9: Full-Duplex Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207

BCR16: I/O Base Address Lower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207

BCR17: I/O Base Address Upper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208

BCR18: Burst and Bus Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208

BCR19: EEPROM Control and Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .209

BCR20: Software Style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212

BCR22: PCI Latency Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214

BCR23: PCI Subsystem Vendor ID Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

BCR24: PCI Subsystem ID Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215

BCR25: SRAM Size Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215

BCR26: SRAM Boundary Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215

BCR27: SRAM Interface Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .216

BCR28: Expansion Bus Port Address Lower (Used for Flash/EPROM and SRAM Accesses). . 216

BCR29: Expansion Port Address Upper (Used for Flash/EPROM Accesses) . . . . . . . . . . . . . . 216

BCR30: Expansion Bus Data Port Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217

BCR31: Software Timer Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217

BCR32: MII Control and Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217

BCR33: MII Address Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .219

BCR34: MII Management Data Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .220

BCR35: PCI Vendor ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

BCR36: PCI Power Management Capabilities (PMC) Alias Register . . . . . . . . . . . . . . . . . . . . .220

BCR37: PCI DAT A Register Zero (DATA0) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221

BCR38: PCI DATA Register One (DATA1) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

BCR39: PCI DATA Register Two (DATA2) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221

BCR40: PCI DATA Register Three (DATA3) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222

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BCR41: PCI DATA Register Four (DATA4) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222

BCR42: PCI DAT A Register Five (DATA5) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

BCR43: PCI DAT A Register Six (DATA6) Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223

BCR44: PCI DATA Register Seven (DATA7) Alias Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

BCR45: OnNow Pattern Matching Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223

BCR46: OnNow Pattern Matching Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224

BCR47: OnNow Pattern Matching Register 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224

Initialization Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225

RLEN and TLEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225

RDRA and TDRA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

LADRF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

PADR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

Receive Descriptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Transmit Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .238

REGISTER SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245

PCI Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245

Memory-Mapped Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

Control and Status Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .248

Bus Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

REGISTER BIT CROSS REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .253

REGISTER PROGRAMMING SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262

Programmable Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266

OPERATING RANGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266

DC CHARACTERISTICS OVER COMMERCIAL OPERATING RANGES . . . . . . . . . . . . . . . . . . . . . . . 267

SWITCHING CHARACTERISTICS: BUS INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .269

SWITCHING WAVEFORMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .270

Key to Switching Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .270

SWITCHING TEST CIRCUITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271

SWITCHING WAVEFORMS: SYSTEM BUS INTERFA CE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272

SWITCHING CHARACTERISTICS: EEPROM INTERFACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .274

SWITCHING CHARACTERISTICS: JTAG TIMING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .276

SWITCHING CHARACTERISTICS: MEDIA INDEPENDENT INTERFACE . . . . . . . . . . . . . . . . . . . . . . 278

SWITCHING CHARACTERISTICS: EXTERNAL ADDRESS DETECTION INTERFACE . . . . . . . . . . .281

SWITCHING WAVEFORMS: RECEIVE FRAME TAG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

SWITCHING WAVEFORMS: EXTERNAL MEMORY INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

PHYSICAL DIMENSIONS* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285

PQFP208. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

Plastic Quad Flat Pack Trimmed and Formed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285

APPENDIX A: LOOK-AHEAD PACKET PROCESSING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Outline of LAPP Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

LAPP Software Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

LAPP Rules for Parsing Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

Some Examples of LAPP Descriptor Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6

Buffer Size Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7

An Alternative LAPP Flow: Two-Interrupt Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-8

APPENDIX B: MII MANAGEMENT REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Control Register (Register 0). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Status Register (Register 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2

Auto-Negotiation Advertisement Register (Register 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

Technology Ability Field Bit Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

Auto-Negotiation Link Partner Ability Register (Register 5). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INDEX-1

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LIST OF FIGURES

Figure 1: Slave Configuration Read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 2: Slave Configuration Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 3: Slave Read Using I/O Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 4: Slave Write Using Memory Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 5: Disconnect Of Slave Cycle When Busy . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 6: Disconnect Of Slave Burst Transfer - No Host Wait States . . . . . . . . . . . . 38

Figure 7: Disconnect Of Slave Burst Transfer - Host Inserts Wait States . . . . . . . . . 39

Figure 8: Address Parity Error Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Figure 9: Slave Cycle Data Parity Error Response . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 10: Bus Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 11: Non-Burst Read Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 12: Burst Read Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 13: Non-Burst Write Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Figure 14: Burst Write Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 15: Disconnect With Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Figure 16: Disconnect Without Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Figure 17: Target Abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 18: Preemption During Non-Burst Transaction . . . . . . . . . . . . . . . . . . . . . . . . 49

Figure 19: Preemption During Burst Transaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Figure 20: Master Abor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Figure 21: Master Cycle Data Parity Error Response . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 22: Descriptor Ring Read In Non-Burst Mode . . . . . . . . . . . . . . . . . . . . . . . . . 53

Figure 23: Descriptor Ring Read In Burst Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Figure 24: Descriptor Ring Write In Non-Burst Mode . . . . . . . . . . . . . . . . . . . . . . . . . 56

Figure 25: Descriptor Ring Write In Burst Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Figure 26: FIFO Burst Write At Start Of Unaligned Buffer . . . . . . . . . . . . . . . . . . . . . 58

Figure 27: FIFO Burst Write At End Of Unaligned Buffer . . . . . . . . . . . . . . . . . . . . . . 59

Figure 28: 16-Bit Software Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 29: 32-Bit Software Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 30: ISO 8802-3 (IEEE/ANSI 802.3) Data Frame . . . . . . . . . . . . . . . . . . . . . . . 70

Figure 31: IEEE 802.3 Frame and Length Field Transmission Order . . . . . . . . . . . . . 73

Figure 32: VLAN-Tagged Frame Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Figure 33: Media Independent Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Figure 34: Frame Format at the MII Interface Connection . . . . . . . . . . . . . . . . . . . . . 83

Figure 35: MII Receive Frame Tagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Figure 36: External SSRAM and Flash Configuration . . . . . . . . . . . . . . . . . . . . . . . . . 92

Figure 37: Expansion ROM Bus Read Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Figure 38: Flash Read from Expansion Bus Data Port . . . . . . . . . . . . . . . . . . . . . . . . 95

Figure 39: Flash Write Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Figure 40: EEPROM Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Figure 41: EEPROM Entry Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Figure 42: CRC Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Figure 43: LED Control Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Figure 44: OnNow Functional Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Figure 45: Pattern Match RAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Figure 46: PCI Expansion ROM Base Address Register . . . . . . . . . . . . . . . . . . . . . 117

Figure 47: Address Match Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 27

Figure 48: Normal and Tri-State Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

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Figure 49: CLK Waveform for 5 V Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Figure 50: CLK Waveform for 3.3 V Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Figure 51: Input Setup and Hold Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Figure 52: Output Valid Delay Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

Figure 53: Output Tri-State Delay Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

Figure 54: EEPROM Read Functional Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274

Figure 55: Automatic PREAD EEPROM Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

Figure 56: JTAG (IEEE 1149.1) TCK Waveform for 5 V Signaling . . . . . . . . . . . . . . 276

Figure 57: JTAG (IEEE 1149.1) Test Signal Timing . . . . . . . . . . . . . . . . . . . . . . . . . 277

Figure 58: Transmit Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

Figure 59: Receive Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

Figure 60: MDC Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .279

Figure 61: Management Data Setup and Hold Timing . . . . . . . . . . . . . . . . . . . . . . .280

Figure 62: Management Data Output Valid Delay Timing . . . . . . . . . . . . . . . . . . . . . 280

Figure 63: Reject Timing - External PHY MII @ 25 MHz . . . . . . . . . . . . . . . . . . . . . 281

Figure 64: Reject Timing - External PHY MII @ 2.5 MHz . . . . . . . . . . . . . . . . . . . . . 282

Figure 65: Receive Frame Tag Timing with Media Independent Interface . . . . . . . .283

Figure 66: External Memory Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

Figure A-1: LAPP Timeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

Figure A-2: LAPP 3 Buffer Grouping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

Figure A-3: LAPP Timeline for Two-Interrupt Method . . . . . . . . . . . . . . . . . . . . . . . . . A-9

Figure A-4: LAPP 3 Buffer Grouping for Two-Interrupt Method . . . . . . . . . . . . . . . . A-10

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LIST OF TABLES

Table 1: System Clock Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 2: Slave Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Table 3: PCI Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Table 4: Descriptor Read Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Table 5: Descriptor Write Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Table 6: Receive Address Match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Table 7: Receive Statistics Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Table 8: Transmit Statistics Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Table 9: VLAN Tag Control Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Table 10: VLAN Tag Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Table 11: Auto-Negotiation Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Table 12: MAC Control Pause Frame Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Table 13: FC Pin Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Table 14: FCCMD Bit Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Table 15: SRAM_TYPE Field Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Table 16: LED Default Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Table 17: IEEE 1149.1 Supported Instruction Summary . . . . . . . . . . . . . . . . . . . . . 104

Table 18: BSR Mode Of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Table 19: Device ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Table 20: PCI Configuration Space Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Table 21: Address PROM Space Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Table 22: I/O Map In Word I/O Mode (DWIO = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Table 23: Legal I/O Accesses in Word I/O Mode (DWIO = 0) . . . . . . . . . . . . . . . . . 109

Table 24: I/O Map In DWord I/O Mode (DWIO = 1) . . . . . . . . . . . . . . . . . . . . . . . . . 109

Table 25: Legal I/O Accesses in Double Word I/O Mode (DWIO =1) . . . . . . . . . . . . 109

Table 26: AP_VALUE0: Auto-Poll Value0 Register . . . . . . . . . . . . . . . . . . . . . . . . . 122

Table 27: AP_VALUE1: Auto-Poll Value1 Register . . . . . . . . . . . . . . . . . . . . . . . . . 123

Table 28: AP_VALUE2: Auto-Poll Value2 Register . . . . . . . . . . . . . . . . . . . . . . . . . 123

Table 29: AP_VALUE3: Auto-Poll Value3 Register . . . . . . . . . . . . . . . . . . . . . . . . . 123

Table 30: AP_VALUE4: Auto-Poll Value4 Register . . . . . . . . . . . . . . . . . . . . . . . . . 123

Table 31: AP_VALUE5: Auto-Poll Value5 Register . . . . . . . . . . . . . . . . . . . . . . . . . 123

Table 32: AUTOPOLL0: Auto-Poll0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

Table 33: AUTOPOLL1: Auto-Poll1 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Table 34: AUTOPOLL2: Auto-Poll2 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Table 35: AUTOPOLL3: Auto-Poll3 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Table 36: AUTOPOLL4: Auto-Poll4 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Table 37: AUTOPOLL5: Auto-Poll5 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

Table 38: Receive Ring Base Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

Table 39: Transmit Ring Base Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Table 40: CHIPID: Chip ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Table 41: CHPOLLTIME: Chain Polling Interval Register . . . . . . . . . . . . . . . . . . . . 129

Table 42: CMD0: Command0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

Table 43: CMD2: Command2 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Table 44: CMD3: Command3 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Table 45: CMD7: Command7 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Table 46: CTRL0: Control0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

Table 47: CTRL1: Control1 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Table 48: CTRL2: Control2 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Page 15

7/25/00 Am79C976 15

PRELIMINARY

Table 49: CTRL3: Control3 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Table 50: Software Styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Table 51: DATAMBIST: Memory Built-in Self-Test Access Register . . . . . . . . . . . . 145

Table 52: DELAYED_INT: Delayed Interrupts Register . . . . . . . . . . . . . . . . . . . . . . 147

Table 53: EEPROM_ACC: EEPROM Access Register . . . . . . . . . . . . . . . . . . . . . .148

Table 54: Interface Pin Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Table 55: FLASH_ADDR: Flash Address Register . . . . . . . . . . . . . . . . . . . . . . . . . 150

Table 56: FLASH_DATA: Flash Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Table 57: FLOW: Flow Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

Table 58: IFS1: Inter-Frame Spacing Part 1 Register . . . . . . . . . . . . . . . . . . . . . . . 152

Table 59: INT0: Interrupt0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .153

Table 60: INTEN0: Interrupt0 Enable Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

Table 61: IPG: Inter-Packet Gap Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Table 62: Logical Address Filter Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Table 63: LED0 Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

Table 64: MAX_LAT_A: PCI Maximum Latency Alias Register . . . . . . . . . . . . . . . . 160

Table 65: MIN_GNT_A: PCI Minimum Grant Alias Register . . . . . . . . . . . . . . . . . . 160

Table 66: PADR: Physical Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

Table 67: PAUSE_CNT: Pause Count Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

Table 68: PCIDATA0: PCI DATA Register Zero Alias Register . . . . . . . . . . . . . . . . 161

Table 69: PHY_ACCESS: PHY Access Register . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Table 70: PMAT0: OnNow Pattern Register 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

Table 71: PMAT1: OnNow Pattern Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

Table 72: Receive Protect Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165

Table 73: RCV_RING_LEN: Receive Ring Length Register . . . . . . . . . . . . . . . . . . 165

Table 74: ROM_CFG: ROM Base Address Configuration Register . . . . . . . . . . . . .166

Table 75: SID_A: PCI Subsystem ID Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . 166

Table 76: SRAM Boundary Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Table 77: SRAM Size Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167

Table 78: STAT0: Status0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168

Table 79: Software Timer Value Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Table 80: SVID: PCI Subsystem Vendor ID Shadow Register . . . . . . . . . . . . . . . . . 170

Table 81: TEST0: Test Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

Table 82: VID_A: PCI Vendor ID Alias Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

Table 83: XMT_RING_LEN: Transmit Ring Length Register . . . . . . . . . . . . . . . . . . 171

Table 84: XMTPOLLTIME: Transmit Polling Interval Register . . . . . . . . . . . . . . . . . 172

Table 85: Software Styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

Table 86: Receive Watermark Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

Table 87: Transmit Start Point Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

Table 88: Transmit Watermark Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

Table 89: BCR Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Table 90: EEDET Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

Table 91: Interface Pin Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

Table 92: Software Styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

Table 93: SRAM_BND Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

Table 94: FMDC Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Table 95: APDW Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Table 96: Initialization Block (SSIZE32 = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Table 97: Initialization Block (SSIZE32 = 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Page 16

16 Am79C976 7/25/00

PRELIMINARY

Table 98: R/TLEN Decoding (SSIZE32 = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

Table 99: R/TLEN Decoding (SSIZE32 = 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

Table 100: Receive Descriptor (SWSTYLE = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Table 101: Receive Descriptor (SWSTYLE = 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Table 102: Receive Descriptor (SWSTYLE = 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

Table 103: Receive Descriptor (SWSTYLE = 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

Table 104: Receive Descriptor (SWSTYLE = 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

Table 105: Receive Descriptor, SWSTYLE = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

Table 106: Receive Descriptor, SWSTYLE = 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

Table 107: Receive Descriptor, SWSTYLE = 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

Table 108: Receive Descriptor, SWSTYLE = 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

Table 109: Receive Descriptor, SWSTYLE = 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235

Table 110: Transmit Descriptor (SWSTYLE = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Table 111: Transmit Descriptor (SWSTYLE = 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Table 112: Transmit Descriptor (SWSTYLE = 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Table 113: Transmit Descriptor (SWSTYLE = 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Table 114: Transmit Descriptor (SWSTYLE = 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

Table 115: Transmit Descriptor, SWSTYLE = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

Table 116: Transmit Descriptor, SWSTYLE = 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

Table 117: Transmit Descriptor, SWSTYLE = 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

Table 118: Transmit Descriptor, SWSTYLE = 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

Table 119: Transmit Descriptor, SWSTYLE = 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

Table 120: Register Bit Cross Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

Table 121: Control and Status Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

Table 122: Bus Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

Table B-1: MII Management Register Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Table B-2: MII Management Control Register (Register 0) . . . . . . . . . . . . . . . . . . . . B-1

Table B-3: MII Management Status Register (Register 1) . . . . . . . . . . . . . . . . . . . . . B-2

Table B-4: Auto-Negotiation Advertisement Register (Register 4) . . . . . . . . . . . . . . . B-3

Table B-5: Technology Ability Field Bit Assignments . . . . . . . . . . . . . . . . . . . . . . . . . B-3

Table B-6: Auto-Negotiation Link Partner Ability Re gister (Register 5)

- Base Page Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

Page 17

8/01/00 Am79C976 17

PRELIMINARY

ORDERING INFORMATION

Standard Products

AMD standard produc ts are av ailable in sev eral pac kages and operating r anges. T he order number (Valid Combination) is f ormed by a combination of the elements below.

AM79C976

TEMPERATURE RANGE

C = Commercial (0 C to +70 C) I = Industrial (–40 C to 85 C

SPEED OPTION

PACKAGE TYPE

Valid Combinations list configurations planned to be supported in volume for this device. Consult the local AMD sales office to confirm availability of specific valid combinations and to check on newly released combinations.

Valid Combinations

DEVICE NUMBER/DESCRIPTION

Not applicable

K = Plastic Quad Flat Pack (PQR208)

Am79C976 PCnet-Pro 10/100 Mb ps PCI Ethernet Controller

Valid Combinations

AM79C976

KC\WV,

KI\W

ALTERNATE PACKAGING OPTION

\W = Trimmed and formed in a tray

Page 18

18 Am79C976 8/01/00

PRELIMINARY

CONNECTION DIAGRAM (PQR208)

200

199

198

197

196

195

194

193

192

191

190

189

188

187

186

185

184

183

182

181

180

179

178

177

176

175

174

173

171

170

169

168

167

166

165

164

163

162

161

172

156 155 154 153 152 151 150 149 148 147 146 145 144 143 142 141 140 139 138 137 136 135 134 133 132 131 130 129

127 126 125 124 123 122 121 120 119 118 117

128

6162636465666768697071727374757677787980818283848586878890919293949596979899100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

30 31 32 33 34 35 36 37 38 39 40

ERD3/FLD3

ERD17 VDD ERD18 ERD19

VSSB

TX_EN

TXD2

ERD0/FLD0 ERD1/FLD1

TXD1

TXD0

VSSB

CRS

VDD

ERD2/FLD2 VDD

ERD4/FLD4 ERD5/FLD5 ERD6/FLD6 VSS

ERD7/FLD7 VDD ERD8/FLA20

ERD10/FLA22 ERD11/FLA23 VSSB

VDD ERD13 ERD14 ERD15 ERD16 VSS

ERD12

ERD9/FLA21

VSSB

TXD3 COL

ERD20

VSSB

IRDY

VDD

TRDY STOP

VSSB

PERR

VSS

SERR

PAR VDD

C/BE1

AD15 AD14

AD30 AD29

VDD AD28 AD27 AD26

VSSB

AD25 AD24

C/BE3

VDD

IDSEL

AD23 AD22

VSSB

AD21

AD20

AD19

VDD AD18

AD17 AD16

VSSB

C/BE2

FRAME

DEVSEL

VSS

ERCE

VDD

EROE

VSSB

ERWE/FLWE

ERADV/FLOE

ERADSP/CEN

VSS

VSSB

ERA13/FLA13

ERA3/FLA3

ERA4/FLA4

VDD

ERA5/FLA5

ERA6/FLA6

ERA8/FLA8

ERA9/FLA9

VDD

VSS

VSSB

ERA11/FLA11

ERA12/FLA12

ERA14/FLA14

VDD

VSSB

ERA15/FLA15

VDD

ERA18/FLA18

ERA17/FLA17

VDD

FLCS

VSSB

ERA1/FLA1

ERA7/FLA7

ERA16/FLA16

ERD31

ERA0/FLA0

ERA10/FLA10

ERA2/FLA2

ERA19/FLA19

VDD

VSS

AVDD

VSSB

XTAL1

EAR

VDD

LED0/EEDI

LED2/RXFRTGE

XTAL2

LED3/EEDO/RXFRTGD

VSS

VSSB

CLKSEL0

TEST

VAUX_SENSE

PHY_RST

MDC

RXD3

VSSB

VDD

RXD0

EECS

PME

WUMI

RWU

TCK

TMS

TDO

VSSB

TDI

XCLK

CLKSEL1

MDIO

RXD2

RXD1

LED1/EESK

CLKSEL2

Am79C976

PCnet-PRO

INTA

RST

VDD

CLK

GNT

AD31

VSSB

REQ

41 42 43 44 45 46 47 48

VSSB

AD13 AD12 AD11

VDD AD10

AD9 AD8

53545556575859

AD5

VDD

AD4

AD3

VSSB

AD2

AD1

AD0

116 115 114 113 112 111 110 109

VDD ERD23 ERD24 ERD25

ERD22

ERD21 VSSB

ERCLK

49 50 51 52

VSSB

C/BE0

AD7 AD6

108 107 106 105

VSSB ERD26 VDD ERD27

101

102

103

104

ERD29

VSSB

ERD28

ERD30

160

159

158

157

RX_DV

RX_ER

TX_CLK

RX_CLK

208

207

206

205

204

203

202

201

22929B2

Page 19

8/01/00 Am79C976 19

PRELIMINARY

PIN DESIGNATIONS (PQR208)

Listed By Pin Number

Pin No. Pin Name Pin No. Pin Name Pin No. Pin Name Pin No. Pin Name

1 AD30 53 AD5 105 ERD27 157 TX_CLK 2 AD29 54 VDD 106 VDD 158 RX_ER 3 VDD 55 AD4 107 ERD26 159 RX_CLK 4 AD28 56 AD3 108 VSSB 160 RX_DV 5 AD27 57 VSSB 109 ERCLK 161 RXD0 6 AD26 58 AD2 110 ERD25 162 VDD 7 VSSB 59 AD1 111 ERD24 163 RXD1 8 AD25 60 AD0 112 ERD23 164 VSSB 9 AD24 61 ERCE 113 VDD 165 RXD2 10 C/BE3 62 VDD 114 ERD22 166 RXD3 11 VDD 63 EROE 115 VSSB 167 MDC 12 IDSEL 64 VSSB 116 ERD21 168 MDIO 13 AD23 65 ERWE/FLWE 117 ERD20 169 PHY_RST 14 AD22 66 ERADV/FLOE 118 ERD19 170 VAUX_SENSE 15 VSSB 67 ERADSP/CEN 119 ERD18 171 TEST 16 AD21 68 VSS 120 VDD 172 CLKSEL0 17 VSS 69 FLCS 121 ERD17 173 CLKSEL1 18 AD20 70 VDD 122 VSSB 174 VSSB 19 AD19 71 ERA0/FLA0 123 VSS 175 CLKSEL2 20 VDD 72 VSSB 124 ERD16 176 VSS 21 AD18 73 ERA1/FLA1 125 ERD15 177 XTAL2 22 AD17 74 ERA2/FLA2 126 ERD14 178 XTAL1 23 AD16 75 ERA3/FLA3 127 ERD13 179 AVDD 24 VSSB 76 ERA4/FLA4 128 VDD 180 XCLK 25 C/BE2 77 VDD 129 ERD12 181 VDD

26 FRAME

78 ERA5/FLA5 130 VSSB 182

LED3

/EEDO/

RXFRTGD

27 IRDY

79 VSSB 131 ERD11/FLA23 183 LED2/RXFRTGE 28 VDD 80 ERA6/FLA6 132 ERD10/FLA22 184 LED1/EESK 29 TRDY 81 ERA7/FLA7 133 ERD9/FLA21 185 LED0/EEDI 30 DEVSEL 82 ERA8/FLA8 134 ERD8/FLA20 186 EECS 31 STOP 83 ERA9/FLA9 135 VDD 187 EAR 32 VSSB 84 VDD 136 ERD7/FLD7 188 VSSB 33 PERR 85 ERA10/FLA10 137 VSSB 189 VSS 34 VSS 86 VSS 138 VSS 190 FC

Page 20

20 Am79C976 8/01/00

PRELIMINARY

35 SERR 87 VSSB 139 ERD6/FLD6 191 VDD 36 PAR 88 ERA11/FLA11 140 ERD5/FLD5 192 PME 37 VDD 89 ERA12/FLA12 141 ERD4/FLD4 193 WUMI 38 C/BE1 90 ERA13/FLA13 142 ERD3/FLD3 194 RWU 39 AD15 91 ERA14/FLA14 143 VDD 195 TCK 40 AD14 92 VDD 144 ERD2/FLD2 196 TMS 41 VSSB 93 ERA15/FLA15 145 VSSB 197 TDO 42 AD13 94 VSSB 146 ERD1/FLD1 198 TDI 43 AD12 95 ERA16/FLA16 147 ERD0/FLD0 199 VSSB 44 AD11 96 ERA17/FLA17 148 CRS 200 PG 45 VDD 97 ERA18/FLA18 149 COL 201 INTA 46 AD10 98 ERA19/FLA19 150 VDD 202 RST 47 AD9 99 VDD 151 TXD3 203 VDD 48 AD8 100 ERD31 152 TXD2 204 CLK 49 VSSB 101 VSSB 153 VSSB 205 GNT 50 C/BE0 102 ERD30 154 TXD1 206 REQ 51 AD7 103 ERD29 155 TXD0 207 VSSB 52 AD6 104 ERD28 156 TX_EN 208 AD31

Pin No. Pin Name Pin No. Pin Name Pin No. Pin Name Pin No. Pin Name

Page 21

8/01/00 Am79C976 21

PRELIMINARY

PIN DESIGNATIONS

Listed By Group

Pin Name Pin Function Signal Type1Pin Type1No. of Pins Clock Interface

XTAL1 Crystal I I 1 XTAL2 Crystal O O 1 XCLK External Clock I I 1 CLKSEL0 Clock Select I I 1 CLKSEL1 Clock Select I I 1 CLKSEL2 Clock Select I I 1 TEST Test Select I I 1

PCI Bus Interface

AD[31:0] Address/Data Bus IO IO 32 C/BE[3:0] Bus Command/Byte Enable IO IO 4 CLK Bus Clock I I 1 DEVSEL Device Select IO IO 1 FRAME Cycle Frame IO IO 1 GNT Bus Grant I I 1 IDSEL Initialization Device Select I I 1 INTA Interrupt O TSO 1 IRDY Initiator Ready IO IO 1 PAR Parity IO IO 1 PERR Parity Error IO IO 1 REQ Bus Requ es t O TSO 1 RST Reset I I 1 SERR System Error IO IO 1 STOP Stop IO IO 1 TRDY Target Ready IO IO 1

Board Interface

LED0 LED0 O TSO 1 LED1 LED1 O TSO 1 LED2 LED2 O IO 1 LED3 LED3 O IO 1 PHY_RST Reset to PHY O O 1 FC Flow Control I I 1

EEPROM Interface

Page 22

22 Am79C976 8/01/00

PRELIMINARY

EECS Serial EEPROM Chip Select O O 1 EEDI Serial EEPROM Data In O TSO 1 EEDO Serial EEPROM Data Out I IO 1 EESK Serial EEPROM Clock IO TSO 1

External Memory Interface

ERCLK External Memory Clock O O 1 ERA[19:0]/FLA[19:0] External Memory Address[19:0] O O 20

ERD[31:0] / FLA[23:20] / FLD[7:0]

External Memory Data [31:0]/Flash Address[23:20]/Flash Data[7:0]

IO IO 32

ERADV

/FLOE Extern al Memory Advance O O 1 ERADSP/CEN External Memory Address Strobe O O 1 EROE External Memory Output Enable O O 1 ERWE/FLWE External Memor y Write En able O O 1 ERCE SSRAM Chip Enable O O 1 FLCS Flash Memory Chip Select O O 1

Media Independent Interface (MII)

COL Collision I I 1 CRS Carrier Sense I I 1 FC Hardware Flow Control I I 1 MDC Management Data Clock O O 1 MDIO Management Data I/O IO IO 1 RX_CLK Receive Clock I I 1 RXD[3:0] Receive Data I I 4 RX_DV Receive Data Valid I I 1 RX_ER Receive Error I I 1 TX_CLK Transmit Clock I I 1 TXD[3:0] Transmit Data O O 4 TX_EN Transmit Data Enable O O 1

External Address Detection Interface (EADI)

EAR External Address Reject I I 1 SFBD Start Frame Byte Delimiter Note 2 Note 2 1 RXFRTGD Receive Frame Tag Data I IO 1 RXFRTGE Receive Frame Tag Enable I IO 1

Power Management Interface

RWU Remote Wake Up O TSO 1 PME Power Management Event O OD 1 WUMI Wake-Up Mode Indicator O OD 1 PG Power Good I I 1

Pin Name Pin Function Signal Type

Pin Type1No. of Pins

Page 23

8/01/00 Am79C976 23

PRELIMINARY

Notes:

1. Since some pins provide more than one signal, the pin type for a signal may differ from the signal type.

2. The SFBD signal can be programmed to appear on any of the LED pins.

Table Legend:

VAUX_SENSE Vaux Sense I I 1

IEEE 1149.1 Test Access Port Interface (JTAG)

TCK Test Clock I I 1 TDI Test Data In I I 1 TDO Test Data Out O O 1 TMS Test Mode Select I I 1

Power Supplies

VDD Digital and I/O Buffer Power P P 24 VSS Digital Ground P P 8 A VDD Analog VDD for PLL and OSC P P 1 VSSB I/O Buffer Ground P P 25

Pin Name Pin Function Signal Type1Pin Type1No. of Pins

Name Pin Type

IO Input/Output

I Input

O Output

TSO Three-State Output

OD Open Drain

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24 Am79C976 8/01/00

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PIN DESCRIPTIONS

PCI Interface

AD[31:0]

Address and Data Input/Output

Address and data ar e multi pl exed on the same bus interface pins. During the firs t clock of a transaction, AD[31:0] contain a physical address (32 bits). During the subsequent clocks, AD[31:0] contain data. Byte ordering is L ittle Endian by de fault. AD[7:0] are de fined as the least significant byte (LSB) and AD[31:24] are defined as the most significant byte (MSB). For FIFO data transfers, the Am79C976 controller can be programmed for Big Endian byte ordering. See Control 0 Register, bit 24 (BSWP) for more details.

During the address phase of the transaction, when the Am79C976 controller is a bus master, AD[31:2] will address the active Double Word (DWord). The Am79C976 controller always drives AD[1:0] to “00” during the address phase indicating linear burst order. When the Am79C976 controller is not a bus master, the AD[31:0] lines are continuously monitored to determine if an address match exists for slave transf ers.

During the data phase of the transaction, AD[31:0] are driven by the Am79C976 controller wh en performing bus master write and slave read operations. Data on AD[31:0] is latched by the Am79C976 co ntroller when performing bus master read and slave write operations.

The Am79C976 device suppor ts Dual A ddress Cy cles (DAC) for systems with 64-bit addressing. As a bus master the Am79C976 d evice wil l gene rate add re ss es of up to 40 bits in length. If the value of the C/BE

[3:0] bus during the PCI addres s phase is 1101b, the address phase is extended to two clock cycles. T he low order address bits appear on the AD[31:0] bus during the first clock cycle, and the high order bits appear during the second clock cycle. In dual address cycles the PCI bus command (memory read, I/O write, etc.) appears on the C/BE

pins during the second clock cycle.

C/BE[3:0]

Bus Command and Byte Enables Input/Output

Bus command and byte enables are multiplexed on the same bus interface pins. During the a ddress phase o f the transaction, C /BE

[3:0] define the bus command.

During the data phase, C/BE

[3:0] are us ed as byte enables. The byte enables define which physical byte lanes carry meaningful data. C/BE

0 applies to byte 0

(AD[7:0]) and C/BE

3 applies to byte 3 (AD[31:24]). The function of the byte enables is indepe nden t of the byte ordering mode (BSWP, CSR3, bit 2).

CLK

Clock Input

This cloc k is us e d to d rive the system b u s i n te rface. All bus signals are sampled on the rising edge of CLK and all parameters are defined with respect to this edge. The Am79C976 controller normally operates over a frequency range of 15 MHz to 33 MHz on the PCI bus due to networking demands. The Am79C976 controller will support a c lock frequency of 0 MHz after cer tain pr ecautions are taken to ens ure data integr ity. This clock or a derivation is not used to drive any network functions.

DEVSEL

Device Select Input/Output

The Am79C976 controller dr ives DEVSEL when it detects a transaction that selects the device as a tar get. The device samples DEVSEL

to detect if a target claims a transaction that the Am79C976 controller has initiated.

FRAME

Cycle Frame Input/Output

FRAME is driven by the Am79 C976 controll er when it is the bus master to indicate the beginning and duration of a transaction. FRAME

is asser ted to indica te a bus

transaction is be ginning. FRAME

is asserted while

data transfers continue. FRAME

is deasserted before the final data phase o f a transaction. When the Am79C976 controller is in slave mode, it samples FRAME

to determ ine the ad dress phas e of a tran sac-

tion.

GNT

Bus Grant Input

This signal indicates that the access to the bus has been granted to the Am79C976 controller.

The Am79C976 controller supports bus parking. When the PCI bus is idle and the system arbiter asserts GNT without an active REQ from the Am79C976 controller, the device will drive the AD[31:0], C/BE

[3:0], and PA R

lines.

IDSEL

Initialization Device Select Input

This signal is used as a chi p sele ct for the Am7 9C97 6 controller duri ng configurat ion read a nd write transactions.

INTA

Interrupt Request Output

An attention signal which indicates that one or more enabled interrupt flag bits are set. See the descriptions of the INT and INTEN registers for details.

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By default INTA

is an open-drain output. For applications that need an a ctive-high edge-sens itive interrup t signal, the INTA

pin can be configured for this mode by

setting INTLEVEL (CMD3, bit 13 or BCR2, bit 7) to 1.

IRDY

Initiator Ready Input/Output

IRDY indicates the ability of the initiato r of the transac tion to complete the current data phase. IRDY

is used

in conjunc ti o n w i th TRDY

. Wait states are inserted until

both IRDY

and TRDY are asser ted simultaneously. A data phase is completed on any clock when both IRDY and TRDY are asserted.

When the Am79C976 c ontroll er is a bus mas ter, it asserts IRDY during all write data phases to indicate that valid data is present on AD[31:0]. Dur ing all read dat a phases, the device asserts IRDY

to indicate that it is

ready to accept the data. When the Am79C976 controller is the target of a trans-

action, it checks IRDY

during all wr ite data phas es to determine if valid data is presen t on AD[31:0]. During all read data phases, the device checks IRDY

to deter-

mine if the initiator is ready to accept the data.

PAR

Parity Input/Output

Parity is even parity across AD[31:0 ] and C/BE[3:0]. When the Am79C976 controller is a bus master, it generates parity during the address and write data phases. It checks parity during read data phases. When the Am79C976 controller operates in slave mode, it checks parity during every address phase. When it is the target of a cycle, it checks parity during write data phases and it generates parity during read data phases.

PERR

Parity Error Input/Output

During any slave write transaction and any master read transaction, the Am79C976 contro ller asserts PE RR when it detects a dat a pa rity error and repo rting of th e error is enabled by setting PERREN (PCI Command register, bit 6) to 1. During any master write transaction, the Am79C976 controlle r monit ors PERR

to see if the

target reports a data parity error.

REQ

Bus Request Input/Output

The Am79C976 controller asserts REQ pin as a signal that it wishes to become a bus mas ter. REQ

is driven high when the Am79C976 control ler does not request the bus.

RST

Reset Input

When RST is asser ted LOW and the PG pin is HIGH, then the Am79C976 controller performs an internal system reset of the type H_RESET (HARDWARE_RESET, see section on RESET). Immediately after the initial power up, RST

must be held low

for 26µs. At any other time RST

must be held low for a minimum of 30 clock periods to gu arant ee t hat the device is properly reset. While in the H_RESET state, the Am79C976 controller will disable or deassert all outputs. RST

may be asynchronous to clock when as-

serted or deasserted. Asserting RS T disables all of the PCI pins except the

PME

pin.

SERR

System Error Output

During any slave transaction, the Am79C976 controller assert s S ER R

when it detects an address par i ty error, and reporting of the error is enabled by setting PERREN (PCI Command register, bit 6) and SERREN (PCI Command register, bit 8) to 1.

By default SERR

is an open-drain out put. For component test, it can be programmed to be an active-high totem-pole output.

STOP

Stop Input/Output

In slave mode, the Am79C976 controller drives the STOP

signal to inform the bus mas ter to stop the current transaction. In bus master mode, the Am 79C976 controller checks STOP

to determine if the target wants

to disconnect the current transaction.

TRDY

Target Ready Input/Output

TRDY indicates the ability of the target of the tran saction to complete the current data phase. Wait states are inserted until both IRD Y

and TRDY are asserted simultaneously. A data phase is comple ted on any clock when both IRDY

and TRDY are asserted.

When the Am79C976 controller is a bus master, it checks TRD Y during all read data phases to determine if vali d data is present on AD[31: 0]. During all write data phases, the device checks TRDY

to determine if the

target is ready to accept the data. When the Am79C976 controller is the target of a trans-

action, it asser ts TRDY

during all read data pha ses to indicate that valid data is present on AD[31 :0]. Durin g all write data phases, the device asserts TR DY

to indi-

cate that it is ready to accept the data.

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26 Am79C976 8/01/00

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PME

Power Management Event Output, Open Drain

PME is an output that can be used to indicate that a power management event (a Magic Pack et, an OnNow pattern match, or a ch ange in link state) has been detected. The PME

pin is asserted when either:

1. PME_STATUS and PME_EN are both 1,

2. PME_EN_OVR and MPMAT are both 1, or

3. PME_EN_OVR and LCDET are both 1. The PME

signal is asynchronous with respect to the

PCI clock.

Board Interface

Note: Before programmin g the LE D pins, see th e description of LEDPE in BCR2, bit 12.

LED0

LED0 Output

This output is designed to directly drive an LED. By default, LED0

indicates an active link connection. This pin can also be programmed to indicate other network status (see BCR4). The LED0

pin polarity is programma-

ble, but by default it is active LOW. When the LED0

pin polarity is programmed to active LOW, the output is an open drain dri ver. When the LED0

pin polarity is programmed to active HIGH, the output is a totem pole driver.

Note: The LED0

pin is multiplexed with the EEDI pin.

LED1

LED1 Output

This output is designed to directly drive an LED. By default, LED1

indicates receive or transmit activity on the network. This pin can also be programm ed to indic ate other network status (see BCR5). The LED1

pin polarity is programmable, but by default, it is active LOW. When the LED1

pin polarity is programmed to active LOW, the output is an o pen drain driver. When the LED1

pin polar ity is programm ed to acti ve HIGH, the

output is a totem pole driver.

Note: The LED1 pin is multiplexed with the EESK pin.

LED2

LED2 Output

This output is designed to directly drive an LED. By default, LED2

indicates that the network bit rate is 100 Mb/s. This pin can also be programmed to indicate various network status (see BCR6). The LED2

pin polarity is programmable, but by default it is active LOW. When the LED2

pin polarity is programmed to active LOW , the

output is an open d rain driver. When the LED2

pin polarity is pr ogrammed to active HIGH, th e output is a totem pole driver.

Note: The LED2

pin is multiplexed with the RXFRTGE

pin.

LED3

LED3 Output

This output is designed to directly drive an LED. By default, LED3

indicates that a collision has occurred. This pin can also be programmed to indicate o ther ne twork status (see BCR7). The LED3

pin polarity i s programmable, but by default it is active LOW. When the LED 3 pin polarity is programmed to active LOW, the output is an open drain driver. When the LED3

pin polarity is programmed to active HIGH, the output is a totem pole driver.

Special attention must be given to the external circuitry attached to this pin. When thi s pin is used to drive an LED while an EEPROM is used in the system, then buffering may be required between the LED3

pin and the LED circuit. If an LED circuit were directly attached to this pin, it may create an I

OL requirement that could

not be met by the serial EEPROM attached to this pin. If no EEPROM is included i n the system design or l ow current LEDs are used, then the LE D3

signal may be directly connecte d to an LED without buffering. In any case, if an EEPROM is present, there must be a pull-up resistor connected to this pin (10 k

W should be ade-

quate). For more details regarding LED connection, see the section on LED Support.

Note: The LED3

pin is multiplexed with the EEDO and

RXFRTGD pins.

Power Good Input

The PG pin has two functions: (1) it puts the device into Magic Packet mode, and (2) it blocks any resets when the PCI bus power is off.

When PG is LOW and either MPPEN or MPMODE is set to 1, the device enters the Magic Packet mode.

When PG is LOW, a LO W assertion of the PCI RST

will only cause the PCI interface pins (except for PME

) to be put in the high impedance state. The internal logic will ignore the assertion of RST

When PG is HIGH, assertion of the PCI RST

pin causes the controller logic to be reset and the configuration information to be loaded from the EEPROM.

RWU

Remote Wake Up Output

RWU is an output that is asserted either when the controller is in the Magic Packet mode and a Magic Packet frame has been detected, or the controller is in the Link Change Detect mode and a Link Change has been detected.

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This pin can dr ive the external system mana gement logic that causes the CP U to get out of a low power mode of operation. This pin is implemented for designs that do not support the PME

function.

Three bits that are loaded from the EEPROM into CSR116 can program the characteristics of this pin:

1. RWU_POL determines the polarity of the RWU signal.

2. If RWU_GATE bit is set, RWU is forced to the hig h impedance state when PG input is LOW.

3. RWU_DRIVER determines whether the output is open drain or totem pole.

The internal power-on-reset signal forces this output into the high impedance state until after the polarity and drive type have been determined.

WUMI

Wake-Up Mode Indicator Output, Open Drain

This output, which is cap able of drivi ng an LED, is asserted when the device is in Magic Packet mode. It can be used to drive external logic that switches the device power source from the main power supp ly to an auxi liary power suppl y.

VAUX_SENSE

3.3 Vaux Presence Sense Input

The signal on this pin is logically anded with bit 15 of the PCI PMC register when the PMC regist er is read. This pin should norm ally be connected to the PCI

3.3 Vaux pin. This allows the PMC register to indicat e

that the device is capable of suppor ting PME

from the

cold

state only when the 3.3 Vaux pin is supplying

power.

CLKSEL0

Clock Select 0 Input

The Am79C976 system clock can either be driven by an external clock generator connected to the XCLK pin or by an internal clock generator timed by a 25-MHz crystal connected between the XT AL1 and XTAL2 pins. The CLKSEL0 and CLKSEL1 pins select the source of the system clock and the frequency at which the external clock generator must run. In addition, CLKSEL0 and CLKSEL1 determine the frequency of ERCLK, the external SSRAM clock. Table 1 shows the possible combinations.

CLKSEL1

Clock Select 1 Input

the system clock and the frequency at which the external clock generator must run. In addition CLKSEL0 and CLKSEL1 determin e the frequenc y of ERCLK, the external SSRAM clock. Table 1 shows the possible combinations.

CLKSEL2

Clock Select 2 Input

The CLKSEL2 pin must be hel d low dur i ng no rmal operation.

TEST

Test Reset Input

The TEST pin must b e held low dur ing nor mal operation.

XCLK

External Clock Input Input

The Am79C976 system clock can either be driven by an external clock generator connect ed to this pin or by a 25-MHz crystal connected between the XTAL1 and XTAL2 pins, depending on the state of the CLKSEL0 and CLKSEL1 pins. When either CLKSEL0 or CLKSEL1 or both are held high, a 20-, 25-, or

-MHz clock signal must be applied to XCLK as

shown in Table 1. When CLKSEL0 and C LKSEL1 ar e both held low, the XCLK pin should be connected to either VSS or VDD.

Table 1. System Clock Selections

XTAL1

Crystal Input

If the CLKSEL0 and CLKSEL 1 pins are both he ld low, a 25-MHz crystal should be connected between the XTAL1 pin and the XTAL2 pin. This crystal controls the frequency of the internal clock-generator circuit.

If the CLKSEL0 and CLKSEL1 pins ar e not both held low, a 20-, 25-, or

-MHz clock source must be con-

CLKSEL2 CLKSEL1 CLKSEL0

CLOCK

SOURCE

ERCLK

(MHz)

1XX

Design Factory

Test Only.

000

25-MHz

Crystal,

XTAL1,XT

AL2

87.5

001

XCLK, 20

MHz

010

XCLK, 25

MHz

87.5

011

XCLK,

MHz

82.5

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28 Am79C976 8/01/00

PRELIMINARY

nected to the XCLK pin, and the XTAL1 and XTAL2 pins should be connected to VSS.

XTAL1 and XTAL2 are not 5-volt tolerant pins.

XTAL2

Crystal Output

If the CLKSEL0 and CLKSEL 1 pins are both he ld low, a 25 MHz crystal should be connected between the XTAL1 pin and the XT AL2 pin. This crystal controls the frequency of the internal clock generator circuit.

If either the CLKSEL0 or the CLKS EL1 pin or both ar e held high, a 20-, 25-, or

-MHz clock source must be

connected to the XCLK pin, and the XTAL1 and XTAL2 pins should be connected to VSS.

XTAL1 and XTAL2 are not 5-volt tolerant pins.

PHY_RST

PHY Reset Output

PHY_RST is an output pin that is used to reset the external PHY. This output eliminates the need for a fan-out buffer for the PCI RST signal, provides polarity for the specific PHY used, and prevents the resetting of the PHY when the PG input is LOW. The output polarity is determined by the PHY_RST_POL bit (CMD3, bit0), which can be loaded from the EEPROM.

The length of time for which the PHY_RST pin is asserted depends on the number of registers that are loaded from the EEP ROM and the order in whi ch the registers are loaded. Immediately after the PHY_RST_POL bit is loaded from the EEPROM, the PHY_RST pin is asser ted. When the la st register has been loaded from the EEPROM, the PHY_RST pin is deasserted. Each register loaded after the PHY_RST_POL bit is loaded adds about 240 µs to the time that PHY_RST is asserted. If the PHY_RST pin is used to reset an external PHY, the us er should prog ram the EEPROM to make sure that PHY_RST is asserted long enough to meet the requirements of the PHY. The user can in sert d ummy writes to offset 28h to extend the reset period.

Flow Control Input

The Flow Control input signal controls when MAC Control Pause Frames are sent or when half-duplex back pressure is asserted.

EEPROM Interface

EECS

EEPROM Chip Select Output

This pin is designed to directly interface to a serial EEPROM that uses the 93Cxx EE PROM interface protocol. EECS is connected to the EEPROM ’s chip select pin. It is controll ed by either the Am7 9C976 controll er

during command portions of a read of the entire EEPROM, or indirectly by the host system by writing to BCR19, bit 2.

EEDI

EEPROM Data In Output

This pin is designed to directly interface to a serial EEPROM that uses the 93Cxx EEP ROM interface protocol. EEDI is co nnected to the EE PROM’s data input pin. It is control led by either the Am7 9C976 controll er during command portions of a read of the entire EEPROM, or indirectly by the host system by writing to BCR19, bit 0.

Note: The EEDI pin is multiplexed with the LED0

pin.

EEDO

EEPROM Data Out Input

This pin is designed to directly interface to a serial EEPROM that uses the 93Cxx EEP ROM interface protocol. EEDO is con nected to the EEPROM’s data output pin. It is control led by either the Am7 9C976 controll er during command portions of a read of the entire EEPROM, or indirectly by the host system by reading from BCR19, bit 0.

Note: The EEDO pin is multiplexed with the LED3

and

RXFRTGD pins.

EESK

EEPROM Serial Clock Output

This pin is designed to directly interface to a serial EEPROM that uses the 93Cxx EEP ROM interface protocol. EESK is connected to the EEPROM’s clock pin. It is controlled by either the Am79C976 controller directly during a read of the entire EEPROM, or indirectly by the host system by writing to BCR19, bit 1.

Note: The EESK pin is multiplexed with the LED1

pin.

External Memory Interface

ERA[19:0]/FLA[19:0]

External Memory Address [19:0] Output

The ERA[19:0] pins provide addresses for both the external SSRAM and the external boot ROM device.

All ERA[19:0] pin outputs are forced to a constant level to conserve power while no access on the External Memory Bus is being performed.

FLA[23:20]

Boot ROM (Flash) Address [23:20] Output

The FLA[23:20] pins provide the 4 most significant bits of the address for the external boot ROM device.

All FLA[23:20] pin outputs are forced to a constant level to conserve power while no access on the External Memory Bus is being performed.

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Note: The FLA[23:20] pins are multiplexed with the ERD[11:8] pins.

ERD[31:0]/FLD[7:0]

External Memory Data [31:0] Input/Output

The ERD[7:0] pins provide data bits [7:0] for boot ROM accesses. The ERD[31: 0] p ins provid e data bits [ 31:0] for external SSRAM accesses. The ERD[31:0] signals are forced to a constant l evel to conser ve power while no access on the Exter nal Memor y Bus is b eing performed.

Note: The FLA[23:20] pins are multiplexed with the ERD[11:8] pins.

ERCE

External SSRAM Chip Enable Output

ERCE

serves as the chip enable for the external SSRAM. It is asser t ed low when the SSRAM add ress o n the ERA[19:0] pins is valid.

FLCS

Boot ROM Chip Select Output

FLCS serves as the chip select for the boot device. It is asserted low when the boot ROM address on the FLA[23:20] and ERA[19:0] pins is valid.

EROE

External SSRAM Output Enable Output

EROE is asserted active LOW during SS RAM device read operations to allow the SSRAM device to drive the ERD[31:0] data bus. It is deasserted at all other times.

FLOE

Expansion ROM Output Enable Out put

FLOE

is asserted active LOW during boot ROM read operations to allow the boot ROM to drive the ERD[7:0] data bus. It is deasserted at all other times.

Note: The FLOE

pin is multiplexed with the ERADV

pin.

ERWE/FLWE

External Memory Write Enable Output

ERWE provides the write enable for write acc esses to the external SSRAM and the Flash (boot ROM) device.

ERADSP/CEN

External Memory Address Strobe Output

ERADSP provides the address strobe signal to load the address into the external SSRAM.

ERADV

External Memory Address Advance Output

ERADV provides the address advance signal to the external SSRAM. Th is signal is asser ted low during a

burst access to increment the addres s counter in the SSRAM.

Note: The FLOE

pin is multiplexed with the ERADV

pin.

ERCLK

External Memory Clock Output

ERCLK is the reference clock for all synchronous SRAM accesses.

Media Independent Interface

TX_CLK

Transmit Clock Input

TX_CLK is a conti nuous clock input th at provides the timing reference for the transfer of the TX_EN and TXD[3:0] signals out of the Am79C976 device. TX_CLK must provide a nibble rate clock (25% of th e network data rate). Hence, an MII transceiver operating at 10 Mbps must provide a TX_CLK f requency of 2.5 MHz and an MII transceiver operating at 100 Mbps must provide a TX_CLK frequency of 25 MHz.

TXD[3:0]

Transmit Data Output

TXD[3:0] is the nibble-wide MII transmit data bus. V alid data is generated on TXD[3:0] on every TX_CLK rising edge while TX_EN is asser te d. While TX_EN is deasserted, TXD[3:0] values are driven to a 0. TXD[3:0] transitions synchronous to TX_CLK rising edges.

TX_EN

Transmit Enable Output

TX_EN indicates when the Am79C976 device is presenting valid transmit nibbles on the MII. While TX_EN is asserted, the Am79C976 device generates TXD[3:0] on TX_CLK risin g edges. TX_EN is as serted with the first nibble of preamble and remains asserted throughout the duration of a packet until it i s deasser ted pr ior to the first TX_CLK following the final nibble of the frame. TX_EN transitions synchron ous to T X_CLK rising edges.

COL

Collision Input

COL is an input that indicates that a collision has been detected on the network medium.

CRS

Carrier Sense Input

CRS is an input that indicates that a non-idl e medium , due either to transmit or receive activity, has been detected.

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30 Am79C976 8/01/00

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RX_CLK

Receive Clock Input

RX_CLK is a clock input that provides the timing reference for the transfer of the RX_DV, RXD[3:0], and RX_ER signals into the Am79C976 device. RX_CLK must provide a nibble rate clo ck (25% of the network data rate). Hence, an MII transceiver operating at 10 Mbps must provide an RX_ CLK freq uency of 2 .5 MHz and an MII transceiver operating at 100 Mbps must provide an RX_CLK frequency of 25 MHz. When the external PHY switches the RX_CLK and TX_CLK, it must provide glitch-free clock pulses.

RXD[3:0]

Receive Data Input

RXD[3:0] is the nibble-wide MII recei ve data bus. Data on RXD[3:0] is sampled on every rising edge of RX_CLK while RX_DV is asserted. RXD[3:0] is ignored while RX_DV is de-asserted.

RX_DV

Receive Data Valid Input

RX_DV is an input used to indicate that valid, received data is being presented o n the RXD[3:0] pins and RX_CLK is sync hronous to the re ceive data. In order for a frame to be fully received by the Am79C976 device on the MII, RX_DV must be asser ted prior to the RX_CLK rising edge, when the first nibble of the Startof-Frame Delimiter is driven on RXD[3:0], and must remain asserted until after the rising edge of RX_CLK, when the last nibble of the CRC is driven on RXD[3:0]. RX_DV must then be deasserted pri or to the RX _CLK rising edge which follows this final nibble. RX_DV transitions are synchronous to RX_CLK rising edges.

RX_ER

Receive Error Input

RX_ER is an input that indicates that the MII transceiver device has detected a coding error in the receive frame currently being transferred on the RXD[3:0] pins. When RX_ER is asser ted whi le RX_DV is assert ed, a CRC error will be indicated in the receive descriptor for the incoming receive frame. RX_ER is ignored while RX_DV is deasserted. Spec i al co de group s gen erate d on RXD while RX_DV is deasserted are ignor ed (e.g., Bad SSD in TX and IDLE in T4). RX_ER transitions are synchronous to RX_CLK rising edges.

MDC

Management Data Clock Output

MDC is a non-continuous clock output t hat provides a timing referenc e for bits on the MDIO p in. Duri ng MII management por t operations, MDC runs at a nominal frequency of 2.5 MHz. When no management operations are in progress, MDC is driven LOW.

If the MII Management p ort is not use d, the MDC pin can be left floating.

MDIO

Management Data I/O Input/Output

MDIO is the bidirectional M II management port data pin. MDIO is an output during the header portion of the management frame transfers and dur ing the dat a portions of write transfers. MDIO is an input during the data portions of read data transfers. When an operation is not in progress on the management port, MDIO is not driven. M DIO tr ansiti ons fr om the Am79C976 contro ller are synchronous to MDC falling edges.

If the PHY is attached through an MII physical connector, then the MDIO pin should be externally pulled down to VSS with a 10-k

W ±5% resistor. If the PHY is perma-

nently connected, the n the MDIO pin should be externally pulled up to VCC with a 10-k

W ±5% resistor.

External Address Detection Interface

EAR

External Address Reject Input

The incoming frame will be checked against the internally active address detection mechanisms and the result of this check will be OR’d with the value on the EAR pin. The EAR pin acts as an exter nal address ac cept function. The pin value is OR’d with the intern al address detection result to determine if the current frame should be accepted. If EAR

remains high while a frame is being received, the frame will be accepted regardless of the state of the internal address matching logic.

The EAR

pin must not be left unconnecte d. If it is no t

used, it should be tied to VSS through a 10-k

W ±5% re-

sistor.

SFBD

Start Frame-Byte Delimiter Output

An initial rising edge on the SFBD signal indicates that a start of valid data is present on the RXD[3:0] pins. SFBD will go high for one nibble time (400 ns when operating at 10 Mbps and 40 ns when operating at 100 Mbps) one RX_CLK perio d after RX_DV has been asserted and RX _ER is deas serted, and there is the detection of the S FD (Start of Frame Delimiter ) of a received frame.

Data on the RXD[3:0] will be the start of the destination address field. SFBD will subsequently toggle every nibble time (1.25 MHz frequency when operating at 10 Mbps and 12.5 MHz fr equency when o peratin g at 10 0 Mbps), indicating the first nibble of each subsequent byte of the received nibble stream. The RX_CLK should be used in conjunction with t he SFBD to latch the correct data for external addre ss matching. SFBD will be active only during frame reception.

Page 31

8/01/00 Am79C976 31

PRELIMINARY

Note: The SFBD signal can be programmed to appear on any of the LED pins.

RXFRTGD

Receive Frame T ag Data Input

When the EADI is enabled (EADISEL, BCR2, bit 3) and the Receive Frame Tagg ing is enabled (RXFRTG, CSR7, bit 14), the RXFRTGD pin becomes a data input pin for the Receive Frame Tag. See the Receive Frame Tagging section for details.

Note: The RXFRTGD pin is multiplexed with the LED3 and EEDO pins.

RXFRTGE

Receive Frame T ag Enable Input

When the EADI is enabled (EADISEL, BCR2, bit 3) and the Receive Frame Tagg ing is enabled (RXFRTG, CSR7, bit 14), the RXFRTGE pin becomes a data input enable pin fo r the Re ceiv e F rame Tag. See the Receive Frame Tagging section for details.

Note: The RXFRTGE pin is multiplexed with the LED2 pin.

IEEE 1149.1 (1990) Test Access Port Interface

TCK

Test Clock Input

TCK is the clock input for the boundary scan test mode operation. It can operate at a frequency of up to 10 MHz. TCK has an internal pull-up resistor.

TDI

Test Data In Input

TDI is the test da ta input path t o the Am79C976 controller. The pin has an internal pull-up resistor.

TDO

Test Data Out Output

TDO is the test data output path from the Am79C97 6 controller. The pin is tri-stated when the JT AG port is inactive.

TMS

Test Mode Select Input

A serial input bit stream on th e TMS pin is used to define the specific bo undary scan test to b e executed. The pin has an internal pull-up resistor.

Power Supply Pins

AVDD

Analog Power (1 Pin) Power

This power supply pin is used for the internal oscillator and phase-locked loop circuits. This pin must be connected to a +3.3-V supply.

VSSB

I/O Buffer Ground (25 Pins) Power

There are 25 ground pins that are used by the input/ output buffer drivers.

VDD

Digital and I/O Buffer Power (24 Pins) Power

There are 24 power supply pins that are used by the internal digital circuitry and I/O buffers. All VDD pins must be connected to a +3.3 V supply.

VSS

Digital Ground (8 Pins) Power

There are eight ground pins that are used by the internal digital circuitry.

Page 32

32 Am79C976 8/01/00

PRELIMINARY

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System Bus Interface

The Am79C976 controller is des igned to operate as a bus master during nor mal operations. Some slave I/O accesses to t he Am79C976 controller are require d in normal operations as well. Initialization of the Am79C976 controller is achieved through a combination of PCI Configuration Space accesses, bus slave accesses, bus master acces ses, and an opti onal rea d of a serial EEPROM that is performed by the Am79C976 controller. The EEPROM read operat ion is performed through the 93Cxx EE PROM int er face. The ISO 8802-3 (IEEE/A NSI 80 2.3) Eth ernet Address may reside within the serial EEPROM. Some Am79C976 controller configuration registers may also be programmed by the EEPROM read operation.

The Am79C976 controller requires 4 Kbytes of memory address spac e for ac cess to all th e various in ternal registers as well as access to some setup information stored in an external serial EEPROM. For compatibility with previous PCnet family devices, the lower 32 bytes of the register space are al so mapped into I/O sp ace, but some functions of the Am79C976 con troller (such as network sta tistics) are only available in memor y space. The location of the memory or I/O address space claimed by this device is programmed through the base address registers in PCI configuration space.

For diskless stations, the Am79C976 controller supports a ROM or Flash-based (both referred to as the Expansion ROM throughout this specification) boot device of up to 16 Mbyte in size. The host can map the boot device to any memory address that aligns to a device size boundary by modifying the Expansion ROM Base Address regi ster in the PC I configu ration spac e. The Expansion ROM device size is d eter mined by the value set in the ROM-CFG register.

Software Interface

The software interface to the Am79C976 controller is divided into three parts. One part is the PCI configura-

tion registers used to identify the Am79C976 controller and to setup the configuration of the device. The setup information includes the I/O or memory mapped I/O base address, mappin g of the Expansion ROM, an d the routing of the Am 79C9 76 controller interr upt ch annel. This allows for a jumperless implementation.

The second por tion of the so ftware interface is the direct access to the I/O resources of the Am79C976 controller. The Am79C976 control le r r e qui r e s 4 Kbytes of memory add re ss spac e for acces s to al l t he vari ous internal registers as well as access to some setup information stored in an external serial E EP ROM. Fo r com patibility with previous PCne t family devices, the lower 32 bytes of the register space are also mapped into I/O space, but some functions of the Am79C976 controller (such as network s tati stic s) a re onl y available in memory space.

The third por tion of the s oftware interface is the d escriptor and buffer areas that are shared between the software and the Am79C976 cont roller durin g normal network oper ations. The desc riptor area b oundaries are set by the software and do not change du r ing normal network operations. There is one descriptor area for receive activity and there is a separate area for transmit activity. The descriptor space contains relocatable pointers to the networ k frame d ata, and it is use d to transfer frame status from the Am79C976 con troller to the software. The buffer areas are locations that hold frame data for transmission or that acce pt frame data that has been received.

Network Interface

The Am79C976 controller can be connected to an IEEE 802.3 or proprietary network through the IEEE

802.3-compliant Media Independent Interface (MII). The MII is a nibble-wide interface to an external 100-Mbps and/or 10-Mbps transceiver device.

The Am79C976 controller supports both half-duplex and full-duplex operation on the network interface.

Page 33

8/01/00 Am79C976 33

PRELIMINARY

DETAILED FUNCTIONS

Slave Bus Interface Unit

The slave bus interface unit (BIU) controls all accesses to the PCI configuration space, the Control and Sta tus Registers (CSR), the Bu s Configuration Registers (BCR), the Ad dress PROM (APROM) lo cations, and the Expansion ROM. Table 2 shows the response of the Am79C976 controller to each of the PCI commands in slave mode.

Table 2. Slave Commands

Slave Configuration Transfers

The host can access the Am79C976 PCI configuration space with a configuration read or write command. The Am79C976 controller will assert DEVSEL

during the

address phase when IDSEL is asserted, AD[1:0] are both 0, and the access is a configuration cycle. AD[7:2] select the DWord location in the configuration space. The Am79C976 controller requires AD[10:8] to be 0, because it is a si ngle function device. AD[31:11] are “don't care.”

The active bytes within a DWord are determined by the byte enable signals. Eight-bit, 16-bit, a nd 32-bit transfers are supported. DEV SEL

is asserted two clock cy-

cles after the host has asserted FRAME

. All configuration cycles are of fixed length. The Am79C976 controll er will asser t TRDY

on the third or

fourth clock of the data phase. The Am79C976 controller does not support burst trans-

fers for access to configurati on space. When th e host keeps FRAME

asserted for a second data phase, the

Am79C976 controller will disconnect the transfer. When the host tries to access the PCI configuration

space while the automatic r ead of the EEPROM after H_RESET (see section on RESET) is on-going, the Am79C976 control ler will ter minate the access on the PCI bus with a disconnect/retry response.

The Am79C976 controller supports fast back-to-back transactions to different targets. This is indicated by the Fast Back-To-Back Capable bit (PCI Status register, bit 7), which is hardwired to 1. The Am79C976 controller is capable of detecting a configuration cycle even when its address phase immediately follows the data phase of a transaction to a different target withou t any idle state in-between. There will be no contention on the DEVSEL

, TRDY, and STOP signals, since the

Am79C976 controll er asser ts DEV SEL

on the second

clock after FRAME

is asserted (medium timing).

Slave I/O Transfers

After the Am79C976 contr oller is confi gured as an I/O device by setting IOEN (for regular I/O mode) or MEMEN (for memory mapped I/O mode) in the PCI Command register, it starts monito r ing the PCI bus for access to its address space. If configured for regular I/O mode, the Am79C976 controller will look for an address that falls within its 32 bytes of I/O address space (starting from the I/O base address). The Am79C976 controller asserts DEVSEL

if it detects an address match and the acces s is an I /O cy cle. If conf igure d for memory ma pped I/O mode, the Am7 9C976 controller will look for an address that falls within its 4096 bytes of memory address space (starting from the memory mapped I/O base address ). The Am79C 976 contr oller asserts DEVSEL

if it detects an address match and the

C[3:0] Command Use

0000

Interrupt Acknowledge

Not used

0001 Special Cycle Not used

0010 I/O Read

Read of CSR, BCR, APROM, and Reset registers

0011 I/O Write

Write to CSR, BCR, and

APROM 0100 Reserved 0101 Reserved

0110 Memory Read

Memory mapped I/O read of

CSR, BCR, APROM, and

Reset registers read of the

Expansion Bus

0111 Memor y Write

Memory mapped I/O write of

CSR, BCR, and APROM 1000 Reserved 1001 Reserved

1010

Configuration Read

Read of the Configuration

Space

1011

Configuration Write

Write to the Configuration

Space

1100

Memory Read Multiple

Aliased to Memory Read

1101

Dual Address Cycle

Not used

1110

Memory Read Line

Aliased to Memory Read

1111

Memory Write Invalidate

Aliased to Memory Write

AD31-

AD11

AD10 -

AD8

AD7-

AD2

AD1 AD0

Don’t care 0

DWord

index

Page 34

34 Am79C976 8/01/00

PRELIMINARY

access is a memor y cycle. DEVSEL is asserted two clock cycles after the host ha s asser ted F RAME

. See

Figure 11 and Figure 22.

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For compatibility with older members of the PCnet family of controllers, the 32 lowest addresses of the I/O or memory space c laime d by the Am7 9C97 6 device support indirect addressing of internal registers. The Am79C976 controller does not s uppor t burst transfers for access to these locations. When the host keeps FRAME

assert ed for a second data phase in this address range, the Am79 C976 controller will discon nect the transfer. How ev er , the controller does support burst accesses to locations at offsets 32 and above.

Because of the side ef fects of reading the Rese t Register at offset 14h or 18h (de pending on the state of DWIO (CMD2, bit 28)), locations at offsets less than 20h cannot be prefetched.

The Am79C976 controller supp orts fast back-to-back transactions to different targets. This is indicated by the Fast Back-To-Back Capable bit (PCI Status register, bit

7), which is hardw ired to 1. The Am79C97 6 controller is capable of detecting an I/O or a memor y-mapped I/O cycle even when its address phase immediately follows the data phase of a transaction to a different target, without any idle state in-between. There will be no contention on the DEVSEL

, TRD Y , and STOP signals, since

the Am79C976 controller asserts DEVSEL

on the sec-

ond clock after FRAM E

is asserted (medi um timing).

See Figure 33 and Figure 44.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

IDSEL

1 23456

1010

PAR

PAR PAR

DATA

ADDR

22929B3

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

IDSEL

1 23456

1011

PAR

DATA

ADDR

22929B4

The Am79C976 co ntroller will not asser t DEVSE L if it detects an address match, but the PCI command is not of the correct type. In memor y mapped I/O mode, the Am79C976 controller aliases all accesses to the I/O resources of the co mm and types Memory Re ad Mul tip le and Memory Read Line to the basic Memor y Read command. All access es of the typ e Memory Write and Invalidate are aliased to the basic Memory Wr ite com mand. Eight-bit, 16-bit, and 32-bit transactions are supported. The Am79C976 contr oller decodes all 32 address lines to determine which I/O resource is accessed.

The number of wait states added to slave transactions varies. Typical values are shown in the table below:

Slave Transactions

Transaction Type

Read Write

Memory-mapped transactions

I/O-mapped transactions 9 3

Page 35

8/01/00 Am79C976 35

PRELIMINARY

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CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

PAR

ADDR

0010

PAR

1 2345678

109

DATA

PAR

22929B5

Page 36

36 Am79C976 8/01/00

PRELIMINARY

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FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

PAR

ADDR

0111

PAR

1 2345678

109

DATA

PAR

22929B6

Page 37

8/01/00 Am79C976 37

PRELIMINARY

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The Am79C976 device includes an int erface to an optional expansion ROM. The amount of PCI address space claimed by this ROM is deter mi ned by the co ntents of the ROM Configura tion Register, ROM_CFG, which should normally be loaded from the serial EEPROM.

The host must initialize the Expansion ROM Base Address register a t off se t 30 H in the PCI configuration space with a valid addre ss b e fore enabling the access to the device. The Am79C976 controller will not react to any access to the Expansion ROM until bo th MEMEN (PCI Command register, bit 1) and ROMEN (PCI Expansion ROM Base Address register, bit 0) are set to 1. After the Expa nsion ROM is en abled, the Am79C9 76 controller will assert DEVSEL

on all memor y read accesses to th e memory space defi ned by t he contents of the Expansion ROM Base Address register. The Am79C976 controller aliases all accesses to the Expansion ROM of the command types Memory Read Multiple and Memory Read Line to the bas ic Memory Read command. Eight-bit, 16-bit, and 32-bit read transfers are supported.

Since setting MEMEN also enables memory mapped access to the I/O resources, attention must be given the PCI Memor y Mapped I/O B ase Address reg ister before enabling access to the Expansion ROM. The host must set the PCI Memor y Mapped I/O Bas e Address register to a value that prevents the Am79C976 controller from claiming any memory cycles not intended for it.

The Am79C976 controller will always read four bytes for every host Expansion ROM read access. Since this takes more than 16 PCI clock cy cles, the Am79 C976 device will assert STOP

to force a PCI bus retry. Subsequent accesses will be retried until all four bytes have been read from the ROM and stored in an internal temporary register. The timing of the access to the ROM device is determined by the ROMTMG parameter (CTRL0, bits 11-8).

Note: The Expansion ROM must not be read when the Am79C976 controller is r unning (when the RUN bit in CMD0 is set to 1). Any access to the Expansion ROM clears the RUN bit and thereby abruptly stops all network and DMA operations.

When the host tries to write to the Expansion ROM, the Am79C976 controller will claim the cycle. The write op-

eration will have no effect. Writes to the Expansion ROM are done through the BCR30 Expansion Bus Data Port. See the section on the Expansion Bus Inter- face for more details.

During the boot procedure, the system will try to find an Expansion ROM. A PCI system assumes that an Expansion ROM is present when it reads the ROM signature 55H (byte 0) and AAH (byte 1).

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In addition to the normal completion of a transaction, there are three scenarios in which the Am79C976 controller term inates a slave access for which it is the tar get.

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If a slave access to the Am79C976 device takes more than 16 PCI CLK cycles, the Am79C976 device will generate a PCI disc onnect/retry cycle by assertin g STOP

and deasser ting TRDY while keeping DEVSEL asserted. This will free up the PCI bus so that it can be used by other bus masters while the Am79C976 device is busy. See Figure 55.

The Am79C976 controller cannot service any slave access while it is reading the contents of the EEPROM. Simultaneous access is not allowed in order to avoid conflicts, since the EEPROM is used to initialize some of the PCI configuratio n space locations and user-selected BCRs and CSRs. The EEPROM read operation will always happen automatically following H_RESET. (See the H_RESET secti on for more details.) In addition, the host can start the read operation by setting the PREAD bit (BCR19, bit 14). While the EEPROM read is on-going, the Am79C976 controller will disconnect any slave access where it is the target by asserting STOP

together with DEVSEL, while driving TRDY high. STOP

will stay asserted until the end of the cycle.

Note: The I/O and memory slave accesses will only be disconnected if they are enabled by setting the IOEN or MEMEN bit in the PCI Co mmand registe r. Without the enable bit set, the cycles will not b e claimed at all. Since H_RESET clears the IOEN an d ME ME N bi ts for the automatic EEPROM read a fter H_RESET, the disconnect only applies to configuration cycles.

The Am79C976 device will also gen erate PCI disconnect/retry cycles when it is executing a blocking read access to an external PHY register.

Page 38

38 Am79C976 8/01/00

PRELIMINARY

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The Am79C976 controller does not support burst access to the configuration space, the first 32 bytes of its I/O or memory s pace, or to the Expansion Bus. The host indicate s a burst transaction by keeping FRAME asserted during the data phase. When the Am79 C97 6 controller sees FRAME

and IRD Y asserted in the clock

cycle before it wants to assert TRDY

, it also asserts

STOP

at the same t ime. The transfer of th e first data

phase is still successful, since IRDY

and TRDY are

both asserted. See Figure 66.

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If the host is not yet ready when the Am79C976 controller asserts TRDY

, the device will wait for the host to as-

sert IRDY

. When the host asserts IRDY and FRAME is still asserted, the Am79C976 controller will finish the first data phase by deas ser ting TRDY

one clock later.

At the same ti me, it will assert ST OP

to signal a discon-

nect to the host. STOP

will stay asserted until th e host

removes FRAM E

. See Figure 77.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

1 2345

CMD

PAR

PAR PAR

DATA

ADDR

22929B7

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

1 2345

PAR

DATA

1st DATA

22929B8

Page 39

8/01/00 Am79C976 39

PRELIMINARY

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When the Am79C976 control ler is not the current bus master, it samples the AD[31:0], C/BE

[3:0], and the PAR li nes during t he address phase of any PCI command for a parity error. When it detects an address parity error, the controller sets PERR (PCI Status register, bit 15) to 1. When repo r tin g of that erro r is ena bled by setting SERREN (P CI Command register, bit 8) an d PERREN (PCI Command register, bit 6) to 1, the Am79C976 controller also d r ives the SERR

signal low for one clock cycle and sets SERR (PCI Status register, bit 14) to 1. The assertion of SERR

follows the address phase by two clock cycles. The Am79C976 controller will not assert DEVSEL

for a PCI transaction that has an address parity er ror when PERREN and SE RREN are set to 1. See Figure 88.

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During the data phase of an I/O write, memory-mapped I/O write, or configurati on write comm and that selects the Am79C976 controller as target, the device samples the AD[31:0] and C/BE

[3:0] lines for parity on the clock edge, and data is transferred as indicated by the assertion of IRD Y

and TRD Y. PAR is sampled in the following clock cycle. If a parity error is detected and reporting of that error is enabled by setting PERREN (PCI Command register, bit 6) to 1, PERR

is asser ted one clock later. The parity error will always set PERR (PCI Status register, bit 15) to 1 even when PERREN is cleared t o

0. The Am79C976 controller will finish a transaction that has a data parity error in the normal way by asserting TRDY

. The corrupted data will be wr itten to the

addressed location. Figure 9 shows a transaction that suffered a parity error

at the time data was transferred (clock 7, IRDY

and

TRDY

are both asser ted). PERR is dr iven high at the beginning of the data phase and then drops low due to the parity error on clock 9, two clock cycles after the data was transferred. After PERR

is driven low, the

Am79C976 controller drives PERR

high for one clock

cycle, since PERR

is a sustained tri-state signal.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

STOP

1 23456

PAR

DATA

1st DATA

22929B9

FRAME

CLK

SERR

C/BE

DEVSEL

1 2345

PAR

ADDR

1st DATA

CMD

PAR

22929B10

Page 40

40 Am79C976 8/01/00

PRELIMINARY

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Master Bus Interface Unit

The master Bus Interface Unit (BIU) controls the acquisition of the PCI bus and all acc esses to the initi alization block, descriptor rings, and the receive and transmit buffer memory. Table 3 shows the usage o f PCI commands by the Am 79C 976 c ontr o lle r in master mode.

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The Am79C976 logic will determine when a DMA transfer should be initiate d. The first step in any Am79C976 bus master transfer is to acquire ownership of the bus. This task is hand led by synchronous log ic within the BIU. Bus ownership is requested with the REQ

signal and ownership is granted by the arbiter

through the GNT

signal.

Figure 10 shows the Am79C976 controller bus acquisition. REQ is asserted and the arbiter returns GNT while another bus master is transferring data. The Am79C976 controller waits until the bus is idle (FRAME and IRDY deasser ted ) before it star t s driv ing AD[ 31:0] and C/BE

[3:0] on clock 5. FRAME is asserted at clock

5 indicating a valid address and command on AD[31:0]

and C/BE

[3:0]. REQ is deasser ted at the same time

that FRAME

is asserted. Th e Am79C976 controller does not use address steppi ng which is reflected by ADSTEP (bit 7) in the PCI Command register being hardwired to 0.

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There are four primary types of DMA transfers. The Am79C976 controller uses non-burst as well as burst cycles for read and write access to the main memory.

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The Am79C976 controller uses non-burst cycles to access descript ors when SWSTYLE (BCR20, bits 7-0) is 0 or 2. All Am79C976 controller non-burst read accesses are of the PCI command type Memor y Read (type 6). Note that dur ing a non-burst read operation, all byte lanes will always be active. The Am79C976 controller will internally discard unneeded bytes.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

PAR

ADDR

CMD

PAR

1 2345678

109

DATA

PAR

PERR

22929B11

Page 41

8/01/00 Am79C976 41

PRELIMINARY

Table 3. PCI Commands

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The Am79C976 controller typically performs more than one non-burst read transaction within a single bus mastership per iod. FRAME

is dropped between consecu-

tive non-burst read cycles. REQ

, however, stays

asserted until F RAME

is asser ted for the last tran saction. The Am79C976 controller supports zero waitstate read cycles. It asserts IRDY

immediate ly af ter t he address phase and at the same time starts sampling DEVSEL

. Figure 11 shows two non-burst read transactions. The first transaction has zero wait st ates. In the second transaction, the target extends the cycle by asserting TRDY

one clock later.

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The Am79C976 controlle r supports burst mod e for all bus master read operations. To allow burst transfers in descriptor read operations, the Am79C976 controller must be programmed to use SWSTYLE 3, 4, or 5 (BCR20, bits 7-0).

The BIU chooses which PCI command to use as follows:

■ When reading one DWord, use Memory Read.

■ When reading a block of more than one DWord that

does not cross a cache line, use Memory Read Line.

■ When reading a block that crosses a cache line

boundary, use Memory Read Multiple.

C[3:0] Command Use

0000 Interrupt Acknowledge Not used 0001 Special Cycle Not used 0010 I/O Read Not used 0011 I/O Write Not used 0100 Reser ved 0101 Reser ved

0110 Memory Read

Read of the initialization block and descriptor rings

Read of the transmit buffer in non-burst mode 0111 Memory Write Write to the descriptor rings and to the receive buffer 1000 Reserved 1001 Reser ved 1010 Configuration Read Not used 1011 Configuration Write Not used 1100 Memor y Read Multiple Read of descriptor or transmit buffer in burst mode 1101 Dual Address Cycle Used when required 1110 Memory Read Line Read of descriptor or transmit buffer in burst mode 1111 Memory Write Invalidate Burst write of 1 or more complete cache lines to the receive buffer

22929B12

FRAME

CLK

IRDY

C/BE

REQ

GNT

1 2345

CMD

ADDR

Page 42

42 Am79C976 8/01/00

PRELIMINARY

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The FIFO thresholds should be greater than or equal to the cache line size to maximize the use of the MRL and MRM commands . If the PCI bridge s tops a tr ansf er , the Am79C976 device waits until the FIFO threshold co nditions are met before resuming the transfer.

During the address phase of a burst access, AD[1:0] will both be 0 indicating a linear burst order. Note that during a burst read operation, all byte lanes will always be active. The Am79C976 controller will inter nally dis card unneeded bytes.

The Am79C976 controller will always perform only a single burst read transaction per bus mastership period, where transa ction is de fined as one address phase and one or multiple data phases. The Am79C976 controller supports zero wait state read cycles. It asserts IRDY

immediately after the address

phase and at the sa me time starts sampling DEVS EL

FRAME

is deasserted when the next-to-last data

phase is completed. The devi ce ma y ins ert IRDY wait states in the middle of

a burst read transaction. Figure 12 shows a typical burst read acces s. The

Am79C976 controller arb itrates for the bus, is granted

access, reads three 32-bit words (DWord) from the system memory, and then releases the bus. In the example, the memory system extends the data phase of each access by one wait state.

%DVLF1RQ%XUVW:ULWH7UDQVIHU

The Am79C976 controll er uses non-burst cycles to write descriptors when SWSTYLE (BCR20, bits 7-0) is 0 or 2. All Am79C976 controller non-burst write accesses are of the PCI comman d type Memory Wri te (type 7). The byte enable signals indicate the byte lanes that have valid data.The Am 79C976 controller may perform more than one non-burst write transaction within a single bus mastership period. FRAME

is dropped between consecutive non-burst write cycles. REQ

, howe ver , stays asserted until FR AME is asse rted for the last transaction. T he Am79 C976 supp or ts zero wait state write cycles. (See the section Descriptor DMA Transfers for the only exception.) It asserts IRDY immediately after the address phase.

Figure 13 shows two non-burst write transactions. The first transaction has two wait states. The Am79C976 device supports zero wait state non-burst write cycles.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

ADDR

0110

PAR

1 2345678

109

DATA

ADDR

DATA

PAR PAR

PAR

0000

0110

0000

22929B13

Page 43

8/01/00 Am79C976 43

PRELIMINARY

)LJXUH%XUVW5HDG7UDQVIHU

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

ADDR

00001110

PAR

1 2345678

109

DATA

PAR PAR

PAR

22929B14

Page 44

44 Am79C976 8/01/00

PRELIMINARY

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The Am79C976 controlle r supports burst mod e for all bus master write operations. To allow burst transfers in descriptor write operations, the Am79C976 controller must be programmed to use SWSTYLE 3, 4, or 5 (BCR20, bits 7-0).

The controller uses the following rules to determine whether to use the PCI Memory Write (MW) command or the Memory Write and Invalidate (MWI) command for burst write transfers.

— When a transfer starts on a cache line boundary,

and there is at least a cache line of data to transfer, use MWI.

— When a transfer does not star t on a cache l ine

boundary, use MW. (T he external PCI bridge should stop the transfer at the cache line boundary if it can make good us e of the MWI command.)

— Stop the MW I transfer at a cache line boundar y

if there is less than 1 cache line of data left to transfer.

The Receive FIFO threshold should be greater than or equal to the cache line size to maximize the use of the

MWI command. If the PC I bridge stops a transfer, the Am79C976 device waits until the FIFO threshold conditions are met before resuming the transfer.

During the address phase o f a burst write transfer AD[1:0] will both be 0 indicating a linear burst order. The byte enable signals indicate which byte lanes have valid data.

The Am79C976 contr olle r wi ll always perfor m a s ingle burst write transaction per bus mastership period, where transaction is defined as one address phase and one or mult iple dat a phase s. Th e Am79C 976 cont roll er supports zero wait state write cycles when using the Memory Write command. When using Memory Write and Invalidate commands, the device may insert IRDY wait states anywhere in the transaction.

The device asserts IRD Y

immediately after the address

phase and at the s ame tim e starts sampling DEVSEL

FRAME

is deasserted when the next-to-last data

phase is completed. Figure 14 shows a typical burst write access. The

Am79C976 controller arbitrates for the bus, is granted access, and writes four 32-bit words (DWords) to the system memor y and then rel eases the bus. In this ex-

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

ADDR

0111

PAR

1 2345678

109

DATA

ADDR

DATA

PAR

0111

22929B15

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8/01/00 Am79C976 45

PRELIMINARY

ample, the memory system extends the data phase of the first access by one wait st ate. The following three data phases take one clock cycle each, which is determined by the timing of TRDY

'0$%XUVW$OLJQPHQW

The BIU has two programmable features that can improve the DMA performance with PCI bri dges that do not automatically stop burst transfers to align them with cache line boundaries:

1. The Burst Alignment (BA) bit ( CTRL0 , bit 0). When this bit is set, if a burst transfer starts in th e middle of a cache line, the transfer will stop at the first cache line boundary.

2. The Burst Limit Register (CTRL0, bi ts 3:0). This 4bit register limits the maximum length of a burst transfer. If the contents of this registe r are 0, the burst length is limited by the amount of data available or by the amount of FIFO space available.

If the contents of this register are not zero, a burst transfer will end when the transfer has crosse d the number of cache line boundar ies equal to the contents of this register.

7DUJHW,QLWLDWHG7HUPLQDWLRQ

When the Am79C976 controller is a bus master, the cycles it produces on the PC I bus may be terminated by the target in one of three different ways: disconnect with data transfer, disconnect without data transfer, and target abort.

'LVFRQQHFW:LWK'DWD7UDQVIHU

Figure 15 shows a disconnection in which one last data transfer occurs after the target asser ted STOP

. STOP is assert ed on clock 4 to start the te rmination sequence. Data is still transferred during this cycle, since both IRDY

and TRDY are ass erted. The Am79C976 controller terminates the current transfer with the deassertion of FRAME

on clock 5 and of IRDY one clock later. It finally releases the bus on clock 7. The Am79C976 controller will again request the bus after two clock cycles, if it wants to transfer more da ta. The starting address of the new transfer will be the address of the next non-transferred data.



)LJXUH%XUVW:ULWH7UDQVIHU

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

12345678

ADDR

DATA

DATA DATA

0111

PAR

PAR PAR

DATA

PAR

DEVSEL is sampled

22929B16

Page 46

46 Am79C976 8/01/00

PRELIMINARY

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'LVFRQQHFW:LWKRXW'DWD7UDQVIHU

Figure 16 shows a tar get disconne ct seque nce dur ing which no data is transferred. STOP

is asserted on clock

4 without TRDY

being asserted at the sam e tim e. The Am79C976 controller terminates the access with the deassertion of FRAME

on clock 5 and of IRDY one

clock cycle later. It finally releases the bus on clock 7. The Am79C976 controller will again request the bus after two clock cycles to retry the last transfer. The starting address of the new transfer will be the address of the last non-transferred data.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

ADDR

00000111

PAR

0111

23456789

PAR

DATA

STOP

ADDRi+8

DATA

22929B17

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8/01/00 Am79C976 47

PRELIMINARY

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Figure 17 shows a target abort sequ ence. The target asserts DEVSEL

for one clock. It then deasserts

DEVSEL

and asser ts STOP on clock 4. A target can use the target abor t sequence to indicate that it cannot service the data transfer and that it does not want the transaction to be retried. Additionally, the Am79C976 controller cannot make any assumption about the success of the previous data transfers in the current transaction. The Am79C9 76 controller terminates the current transfer with the deassertion of

FRAME

on clock 5 and of IRDY one clock cycle later.

It finally releases the bus on clock 6. Since data integrity is not guaranteed, the Am79C976

controller cannot recover from a target abort event. The Am79C976 controller will reset all CSR locations to their STOP_RESET values. The BCR and PCI configuration registers will not be cleared. Any on-going network transmission is terminated with the current FCS inverted and appended at the next byte boundary. This guarantees that the receiving station will drop the truncated frame.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

STOP

ADDR

00000111

PAR

0111

23456789

ADDR

DATA

PAR

22929B18

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48 Am79C976 8/01/00

PRELIMINARY

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RTABORT (PCI Status register, bit 12) will be set to indicate that the Am 79C976 controller has received a target abort. In addition, SINT (CSR5, bit 11) will be set to 1. When SINT is set , INTA

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There are three scenar ios besides normal comp letion of a transaction wher e the Am79C976 contr oller will terminate the cycles it produces on the PCI bus.

3UHHPSWLRQ'XULQJ1RQ%XUVW7UDQVDFWLRQ

When the Am79C976 controller performs multiple nonburst transactions, it keeps REQ

asser ted until the as-

sertio n of FRAME

for the last transaction. When GNT is removed, the Am79C976 controller will finish the current transaction and then release the bus. If it is not the last transaction, REQ

will remain asserted to regain

bus ownership as soon as possible. See Figure 1818.

3UHHPSWLRQ'XULQJ%XUVW7UDQVDFWLRQ

When the Am79C976 controller operates in burst mode, it only performs a single transaction per bus mastership period, where transaction is defined as one address phas e and one or mu ltiple data p hases. The central arbiter can remove GNT

at any time dur ing th e transaction. The Am79C976 controller will ignore the deasser tion of GNT

and continue w ith data t ransfers, as long as the PCI Latency Timer is not expired. When the Latency Timer is 0 and GNT

is deasserted, the Am79C976 controller will finish the current data phase, deassert FRAM E

, finish the last data pha se, and re-

lease the bus. It will immediately assert REQ

to regain

bus ownership as soon as possible. When the pree mption occurs af ter the counter has

counted down to 0, the Am79C976 controller will finish the current data phase, deass ert FR AME

, finish the last data phase, and release the bus. Note that it is important for the host to program the PCI Lat ency Timer according to the bus bandwidth requirement of the Am79C976 controller. The host can determine this bus bandwidth requirement by reading the PCI MAX_LAT and MIN_GNT registers.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

234567

ADDR

0000

0111

PAR PAR

DATA

STOP

22929B19

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8/01/00 Am79C976 49

PRELIMINARY

)LJXUH3UHHPSWLRQ'XULQJ1RQ%XUVW7UDQVDFWLRQ

If the controller is executing a Memory Write and Invalidate instructio n when preemptio n occurs, the contro ller will finish writing the current cache line before it releases the bus.

Figure 19 assumes that the PCI Latency Timer has counted down to 0 on clock 7.

0DVWHU$ERUW

The Am79C976 controller will terminate its cycle with a Master Abort sequence if DEVSEL

is not asserted

within 4 clocks after FRAME

is asserted. Master Abort is treated as a fatal error by the Am79C9 76 controll er. The Am79C976 cont roller will rese t all CSR locatio ns to their STOP_RESET values. The BCR and PCI configuration registers will not be clea red. Any on-going

network transmissi on is terminated in an orderly sequence. The message wi ll have the current FCS inverted and appended at the next byte boundary to guarantee that the receiving station will treat the transmission either as a runt or as a corrupted frame.

RMABORT (in the PCI Status register, bit 13) will be set to indicate that the Am79C976 controller has terminated its transaction with a master abort. In addition, SINT (CSR5, bit 11) will be set to 1. When SINT is set, INTA

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

1 234567

BE0111

PAR

DEVSEL is sampled

PAR

DATA

ADDR

22929B20

Page 50

50 Am79C976 8/01/00

PRELIMINARY

)LJXUH3UHHPSWLRQ'XULQJ%XUVW7UDQVDFWLRQ

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

PAR

DEVSEL is sampled

ADDR

BE0111

PAR

1 234

DATA

PAR

REQ

DATA

PAR PAR PAR

PAR

GNT

22929B21

Page 51

8/01/00 Am79C976 51

PRELIMINARY

)LJXUH0DVWHU$ERU

3DULW\(UURU5HVSRQVH

During every data phase of a DMA r ead operation, when the target in dicates that the data is valid by asserting TRDY

, the Am79C976 controller samples the

AD[31:0], C/BE

[3:0] and the PAR lines for a data parity error. When it detects a data parity error, the controller sets PERR (PCI Status regi ster, bit 15) to 1. When reporting of th at error is enabled by setting PERREN (PCI Command register, bit 6) to 1, the Am79C976 controller also drives the PERR

signal low and sets DATAPERR (PCI Status register, bit 8) to 1. The assertion of PERR

follows the corrupted data/byte enables

by two clock cycles and PAR by one clock cycle.

Figure 21 shows a transaction that has a parity error in the data phase. The Am79C976 controller asser ts PERR

on clock 8, two clock cycles after data is valid. The data on clock 5 is not checked for parity, since on a read access PAR is only required to be valid one clock after the target has asserted TRDY

. The

Am79C976 controller then drives PERR

high for one

clock cycle, since PERR

is a sustained tri-state signal.

During every data phase of a DMA write operation, the Am79C976 controll er checks the P ERR input t o see if the target reports a parity error. When it sees the PERR input asserted, the controller sets PERR (PCI Status register, bit 15) to 1. When PERREN (PCI Command register, bit 6) is set to 1, the Am79C976 controller also sets DATAPERR (PCI Status register, bit 8) to 1.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

PAR

DEVSEL is sampled

ADDR

0111

PAR

1 234

DATA

PAR

REQ

GNT

0000

22929B22

Page 52

52 Am79C976 8/01/00

PRELIMINARY

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Whenever the Am79C976 controller is the cur rent bus master and a da t a pa rity er r o r o ccu rs, SINT (CS R5, b it

11) will be set to 1. When SINT is set, INTA

is asserted if the enable bit SINTE (CSR5, bi t 10) is set to 1 . This mechanism can be used to inform the driver of the system error. The host can read the PCI Status register to determine the exact cause of the interr u pt. Th e sett in g of SINT due to a data par ity e rror is not d ependen t o n the setting of PERREN (PCI Command register, bit 6).

By default, a data parity error does not affect the state of the MAC engine. The Am79C976 controller treats the data in all bus master transfers that have a parity error as if nothing has happened. All network activity continues.

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During execution of the Am79C976 controller bus master initializatio n procedure, the Am79C97 6 controller

will use a burst transfer of seven Dwords to read the initialization block. AD[1:0] is 0 during the address phase indicating a linear burst order.

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During descri ptor read accesses, the byte enable signals will indicate that all byte lanes ar e active. Should some of the bytes not be needed, then the Am79C976 controller will internally discard the extraneous information that was gathered during such a read.

The settings of SWSTYLE (BCR20, bits 7-0) affect the way the Am79C976 controller performs descriptor read operations.

Because of the order in which the descriptor data must be read or written when SWSTY LE is set to 0 or 2, all descriptor read o perations ar e performed in non -burst mode. See Figure 2222.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

PAR

DEVSEL is sampled

ADDR

0111

PAR

1 234

DATA

PAR

PERR

22929B23

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8/01/00 Am79C976 53

PRELIMINARY

)LJXUH'HVFULSWRU5LQJ5HDG,Q1RQ%XUVW0RGH

When SWSTYLE i s se t to 3, 4, or 5 the desc ri ptor e ntries are ordered to allow burst transfers, and the Am79C976 controller will perfor m all descriptor read

operations in burst mo de. The device may read more than one descriptor in a single burst. See Figure 23.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

MD1

00000110

PAR

DATA DATA

MD0

00000110

PAR PAR

1 2345678

109

22929B24

Page 54

54 Am79C976 8/01/00

PRELIMINARY

)LJXUH'HVFULSWRU5LQJ5HDG,Q%XUVW0RGH

Table 4 shows the descriptor read sequence. During descriptor write ac cesses, only the byte lanes which need to be written are enabled.

The settings of SWSTYLE (BCR20, bits 7-0) affect the way the Am79C976 controller performs descriptor write operations.

When SWSTYLE is set to 0 or 2, all descriptor write operations are performed in non-burst mode.

When SWSTYLE is set to 3, 4, or 5, the descriptor entries are ordered to allow burst transfers. The Am79C976 controller will perform all descriptor write operations in burst mode. See Tab le 5 for the descriptor write sequence.

Table 4. Descriptor Read Sequence

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

1 234567

MD1

00000110

PAR

PAR PAR

DATA

PAR

DEVSEL is sampled

22929B25

SWSTYLE

BCR20

[7:0]

AD Bus Sequence for Rx Descriptors

AD Bus Sequence for Tx Descriptors

Address = XXXX XX00h

Turn around cycle Data Idle Address = XXXX

XX04h Turn around cycle Data

Address = XXXX XX00h

Turn around cycle Data Idle Address = XXXX

XX04h Turn around cycle Data

Address = XXXX XX04h

Turn around cycle Data Idle Address = XXXX

XX00h Turn around cycle Data

Address = XXXX XX04h

Turn around cycle Data Idle Address = XXXX

XX00h Turn around cycle Data

Address = XXXX XX04h

Turn around cycle Data Data

Address = XXXX XX04h

Turn around cycle Data Data

Address = XXXX XX04h

Turn around cycle Data Data

Address = XXXX XX00h

Turn around cycle Data Data Data

Address = XXXX XX08h

Turn around cycle Data Data Data

Address = XXXX XX00h

Turn around cycle Data Data Data Data

Page 55

8/01/00 Am79C976 55

PRELIMINARY

Table 5. Descriptor Write Sequence

Note: Figure 24 assumes that the Am79C976 controller is programmed to use 32-bit software structures (SWSTYLE = 2, 3, 4, or 5). The byte enable signals for the second data transfer would be 011 1b, if the device

was programmed to use 16-bit software structures (SWSTYLE = 0).

SWSTYLE BCR20[7:0]AD Bus Sequence

for Rx Descriptor

AD Bus Sequence for Tx Descriptor

Address = XXXX XX04h

Data Idle Address = XXXX

XX00h Data

Address = XXXX XX04h

Data Idle Address = XXXX

XX00h Data

Address = XXXX XX08h

Data Idle Address = XXXX

XX04h Data

Address = XXXX XX08h

Data Idle Address = XXXX

XX04h Data

Address = XXXX XX00h

Data Data

Address = XXXX XX00h

Data Data

Address = XXXX XX00h

Data

Address = XXXX XX00h

Data

Address = XXXX XX00h

Data

Address = XXXX XX00h

Data

Page 56

56 Am79C976 8/01/00

PRELIMINARY

)LJXUH'HVFULSWRU5LQJ:ULWH,Q1RQ%XUVW0RGH

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

MD2

00000111

PAR

MD1

00110111

PAR

1 2345678

109

DATA

PAR

DATA

22929B26

Page 57

8/01/00 Am79C976 57

PRELIMINARY

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),)2'0$7UDQVIHUV

Am79C976 logic will determine when a FIFO DMA transfer is required. This transfer mode will be used for transfers of data to and fro m the Am79C976 FIFO s. Once the Am79C976 BI U has been granted bus mastership, it will perform a series of co nsecutive transfer cycles before relinquishing the bus. All transfers within the master cycle will be either read or write cycles, and all transfers will be transferred to contiguo us, ascending addresses. Burst cy cles ar e use d whenever possible.

A burst transaction will start with an address phase, followed by one or more data phases. AD[1:0] will always be 0 during the address phase indicating a linear burst order.

During FIFO DMA read operations, all byte lanes will always be active. The Am79C976 co ntroller will internally discard unused bytes. During the first and the last data phases of a FIFO DMA burst write operation, one or more of the byte enable s ig nal s may be in active. All other data phases will always write a complete DWord.

Figure 26 shows the beginning of a FIFO DMA write with the beginning of the buffer not aligned to a DWord boundary. The Am79C976 controller star ts o ff by wr iting only three bytes during the first data phase. This operation aligns the address for all other data transfers to a 32-bit boundary so that the Am79C976 controller can continue bursting full DWords.

GNT

REQ

DEVSEL

TRDY

PAR

C/BE

FRAME

CLK

PAR

IRDY

DEVSEL is sampled

DATA

1 2 4 6 7 8

0110

0000 0011

MD2

PAR

DATA

PAR

22929B27

Page 58

58 Am79C976 8/01/00

PRELIMINARY

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%XIIHU

If a receive buffer does not end on a DWord boundary, the Am79C976 controller will perform a non-DWord write on the last transfer to the buffer. Figure 27 shows the final three FIFO DMA trans fers to a receive buffer. Since ther e were only 9 bytes of sp ace left in the r eceive buffer , the Am79C976 controller bursts three data phases. The first two data phases writ e a full DWord, the last one only writes a single byte.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

1 23456

00000111

PAR

PAR PAR

DEVSEL is sampled

0001

PAR

DATA DATA

DATA

ADD

22929B28

Page 59

8/01/00 Am79C976 59

PRELIMINARY

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Note that t he Am 7 9C 9 76 controller wi ll al ways pe rform a DWord transfer as long as it owns the buffer space, even when there are less than four bytes to write. For example, if there is only one byte left for the current receive frame, the Am79C976 controller will write a full DWord, containing the last byte of the receive frame in the least signifi cant byte position (BSWP is c leared to 0, CSR3, bit 2). The content of the other th ree bytes is undefined. The message byte count in the receive descriptor always reflects the exact length of the received frame.

In the normal DMA mode (when the Burst Alignment bit = 0 and the Burst Limit register contents = 0) the Am79C976 contro ller will continue transferr ing FIFO data until the transmit FIFO is filled to its high threshold (for read transfers) or the receive FIFO is emptied to its low threshold (for write transfers), or until the Am79C976 controller is preempted and the PCI Latency Timer is expired. The host should use the values in the PCI MIN_GNT and MAX_LAT registers to determine the value for the PCI Latency Timer.

In the burst alignment mode (when the Burst Alignment bit = 1) if a burst transfer starts in the middle of a cache

line, the transfer will stop at the first cache line boundary.

If the contents of the Burst Limit register are not zero, a burst transfer will end when the transfer has crossed the number of cache line bo und aries equal to the c ontents of this register.

The exact number of total transfer cycles in the bus mastership per iod is dependent on all of the following variables: the settings of the FIFO watermarks, the conditions of the FIFOs, the laten cy of the sy stem bus to the Am79C976 controller’s bus requ est, and the speed of bus operation. The TRDY

response time of the memory de vice wil l also affect the number of trans fers, since the speed of the accesses will affect the state of the FIFO. The general rule is that the longer the Bus Grant lat ency, the slower th e bus transfer operations; the slower the clock speed, the hig her th e tran smit watermark; or the lower the receive watermark, the longer the total burst length will be.

When a FIFO DMA burst operation is preempted, the Am79C976 controller wil l not reli nq uis h bus ownershi p until the PCI Latency Timer expires.

Descriptor Management Unit

The Descriptor Management Unit (DMU) implements the automatic initialization procedure and manages the descriptors and buffers.

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The Am79C976 controller is initialized by a combination of EEPROM register writes, direct register writes from the PCI bus and, for compatibility with older PCnet family products, DMA reads f ro m an ini tia li za tio n block in memory . The registers that must be programmed depend on the features that are required in a particular application. See USER ACCESSIBLE REG ISTERS on page 111 for more detail s.

The format of the legacy initialization block depends on the programming of the SWSTYLE register, as described in the Initialization Block section.

The initia lization block is r ead when the IN IT bit in CSR0 is set. The INIT bit shoul d be set before or concurrent with the STRT bit to ensure correct o peration. Once the initia liza tion block has been comp letely rea d in and internal r egisters have been updated, IDON will be set in CSR0, generating an interrupt (if IENA is set).

The Am79C976 con troller obta ins the sta rt address o f the initialization block from the contents of CSR1 (least significant 16 bits o f addr ess) a nd C SR2 (mos t signi ficant 16 bits of address). The host must write CSR1 and CSR2 before setting the INIT bit. The initialization block contains the user defined conditions for Am79C976 operation, together with the base addresses and length information of the transmit and receive descriptor rings.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

1 234567

00000111

PAR

PAR PAR

PAR

DEVSEL is sampled

1110

PAR

DATA DATA

DATA

ADD

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60 Am79C976 8/01/00

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Earlier members of the PCnet family of controllers had to be re-initialized if the transmitter and/or the receiver were not turned on during the original initialization, and it was subsequently requir ed to activate them, or if e ither sectio n was shut of f due to the det ection of a m emory error, transmitter underflow, or transmit buffer error condition. This restr iction does not apply to the Am79C976 device. The memor y error and transmit buffer error conditions cannot occur in the Am79C976 controller and th e transmit underfl ow condition does not stop the Am79C976 controller’s transmitter.

For compatibility with other PCnet family devices, reinitialization may be done v ia the initial ization block or by setting the STOP bit in CSR0, followed by writing to CSR15, and then set ting the STRT bit in CSR0. Note that this form of restart will not perform the same in the Am79C976 controller as in the C-LANCE device. In particul ar, setting the STRT bit causes the Am79C97 6 controller to reload the transm it and rec eive descr iptor pointers with their respective base addr esses. This means that the software must clear the descriptor OWN bits and reset its descri ptor ring point ers before restarti ng the Am79C976 controller. The reload of descriptor base addr esses i s perform ed in the C-LA NCE device only after initialization, so that a restart of the C-LANCE without initialization leaves the C-LANCE pointing at the same descriptor locations as before the restart.

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Following reset, the transmitter and receiver of the Am79C976 controller are disabled, so no descriptor or data DMA activity will occur. The receiver will process incoming frames to detect address matches, which are counted in the RcvMissP kts reg ister. No transmits wi ll occur except that pause frames may be s ent (see fl ow control section).

Setting the RUN bit in CMD0 (equivalent to setting STRT in CSR0) causes the Am79C976 controller to begin descrip tor polling and nor mal transmit and r eceive activity. Clearing the RUN bit (equivalent to setting STOP in CSR0) causes the Am79C976 con troller to halt all transmit, receive, and DMA transfer activities abruptly.

The Am79C976 controller o ffers suspend mode s that allow stopping the device with orderly termination of all network activity. Transmit and receive are controlled separately.

Setting the RX_FAST_SPND bit in CMD0 suspends receiver activity after the current frame being received by the MAC is complete. If no frame is being received when RX_FAST_SPND is set, the receiver is suspended immed iately. After the receiver is suspe nded, the RX_SUSPENDED bit in STAT0 is set and SPNDINT interrupt bit in INT0 is set. Receive data and de-

scriptor DMA activity continues normally while the receiver is fast suspended.

Setting the RX_SPND bit in CMD0 s uspends the receiver in the same way as RX_FAST_SPND, but the RX_SUSPENED b it and SPNDINT inter rupt bit are only set after any frames in the receive FIFO have been completely transferred into system memory and the corresponding descriptors updated. No receive data or descriptor DMA activi ty will o ccur w hile the receiver is suspended.

When the receiver is susp ended, n o frames will be received into the receive FIFO, but frames will be checked for address match and the RcvMissPkts counter increment ed appropr iately, and frames will be checked for Magic Packet match if Magic Packet mode is enabled.

Setting the TX_FAST_SPND bit in CMD0 suspends transmitter activity after the c urrent frame bein g transmitted by the MAC is complete. If no frame is being transmitted when TX_F AST_SPND is set, the transmitter is suspended immediately. After the transmitter is suspended, the TX_SUSPENDED bit in STAT0 is set and SPNDINT interru pt bit i n INT0 is set. Transmit descriptor and data DMA activity c ontinues normally while the transmitter is fast suspended.

Setting the TX_SPND bit in CMD0 suspends the transmitter in the same way as TX_FAST_SPND, but the TX_SUSPENDED bit and SPNDI NT interrupt bit are only set after any frames in the transmit FIFO have been completely transmitted. No transmit descriptor or data DMA activity will occur while the transmitter is suspended.

When the transmitte r is suspended, n o frames will b e transmitted except for flow control frames (see Flow Control section).

It is not meaningful to set both TX_SPND and TX_FAST_SPND at the same time, nor is it meaningful to set both RX_SPND a nd RX_FAST_SPND at the same time. Doing so wil l cause unpredicta ble results. However , transmit and receive are independent of each other, so one may be suspended or fast suspended while the other is running, suspe nded or fast suspended.

For compatibility with other PCne t family devices, setting the SPND bit in CSR5 with FASTSPNDE in CSR7 cleared is equivalent to setting both TX_SPND a nd RX_SPND and clearing SPND with FASTSPNDE cleared is equivalent to clearing both TX_SPND and RX_SPND. Similarly, setting SPND with FASTSPNDE set is equivalent to setting both TX _FAST_SPND and RX_FAST_SPND and clearing SPND with FASTSPNDE set is equivalent to clearing both TX_FAST_SPND and RX_F AST_SPND . While equivalent, these methods ar e not identical, so software

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should not mix the CSR5/CSR7 method with the CMD0 method.

For compatibility with other PCnet family devices, after the SPND bit in CSR5 is set, it will read back a one only after the suspend operation is complete, that is, after both TX_SUSPENDED and RX_SUSPENDED in STAT0 have been set. It is recommended that when software polls this register that a delay be inserted between polls. Continuous po lling will reduce the bus bandwidth available to the Am79C976 controller and will delay the completion of the suspend operation.

It is recommended that so ftware use the SP NDINT interrupt to determine when the Am79C976 controller has suspended after one or more suspend bits have been set. This results in the least competition for the PCI bus and thus the shortest time from setting of a suspend bit until completion of the suspend operation.

Clearing the RUN bit in CMD0 will generate a pulse that will clear all the suspend command and st atus bits (TX_SPND, RX_SPND, TX_FAST_SPND and RX_FAST_SPND in CMD0, TX_SUSPENDED and RX_SUSPENDED in STAT0, SPND in CSR5 and DRX and DTX in CSR15). The RX_SPND or TX_SPND bits may then be set while RUN is cleared. When RUN is subsequently set, the suspend bi t will remain set an d the corresponding operation (transmit or receive) will be disabled. Since the suspend bit will be cleared when RUN is cleared, this must be done each time RUN is set. Since the suspend bits an d RUN are in the same register (CMD0), the suspend bit may be set at the same time that RUN is set.

For compatibility with other PCnet family devices, setting the STOP bit in CSR0 will al so cl ea r the S PND bit in CSR5. While STOP is set, the DRX or DTX bits in CSR15 may be set. When the STRT bit in CSR0 is subsequently set, the corr espon ding op eration wil l be disabled. Since the bits are all cleared when STOP is set, CSR15 must be written (either directly or indirectly via the DMA initialization) ea ch time before STRT is set again.

The suspend bits in CMD0 an d STAT0 are equivalent but not identical to the suspend bits in CSR5, CSR7 and CSR15. Software should use one set of bits or the other and not mix them. The SPNDI NT bit in INT0 has no equivalent in the CSR registers, so this bi t may be used to detect the com pletion of a sus pend operation initiated by the SPND bit in CSR5.

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Descriptor management is accomplished through message descripto r entr ies organized as rin g str uc tures i n memory. There are two descriptor rings, one for transmit and one for receive. Each descriptor describes a single buffer. A frame may occupy one or more buffers.

If multiple buffers are used, this is referred to as buffer chaining.

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Each descriptor ring must occupy a contiguous area of memory. During initialization, the user-defined base address for the transmit and receive descriptor rings, as well as the num ber of entri es contained in the descriptor rings a re s et u p. The programming o f the s oftware style (SWSTYLE, BCR20, bits 7-0) affects the way the descriptor rings and their entries are arranged.

When SWSTYLE is at its default value of 0, the descriptor rings are backwards compatible with the Am79C90 C-LANCE and the Am79C96x PCnet-ISA family. The descriptor r ing base addresses must be aligned to 8-byte boundari es. Each ring entr y co ntai ns a subset of the three 32-bit transmit or receive message descriptor s that are organized as four 16-bit structures (SSIZE32 (BCR20, bit 8) is set to 0). Note that even though the Am79C976 controller treats the descriptor entries as 16-bit structures, it will always perform 32-bit bus transfers to access the descriptor entries. The value of CSR2, bits 15-8, is us ed as the upper 8-bits for all memory addresses during bus master transfers.

When SWSTYLE is set to 2, 3, or 4, the descriptor ring base addresses must be aligned to 16-byte boundaries. Each ring entry is organized as three 32-bit message descriptors (SS IZE32 (BCR20, bit 8) is set to 1) . The fourth DWord is reserved for user software purposes. When SWSTYLE is set to 3, 4, or 5, the order of the message descriptors is optimized to allow read and write access in burst mode.

When SWSTYL E is set to 5, the descri ptor ring ba se addresses must be aligned to a 32-byte boundary. Each ring entry is or ganized as eigh t 32-bit mess age descriptors (SSIZE32 (BCR20, bit 8) is set to 1).

Descriptor ri ng lengths can be s et up either by writin g directly to the transmit and receive ring length registers (CSR76, CSR78) or by using the initialization block. If the initialization block is used to set up ring lengths, the ring lengths are restricted to powers of two that are less than or equal to 128 if SWSTYLE is 0 or 512 if SWSTYLE is 2 or 3. However, ring lengths of any size up to 65535 descriptors can be set up by writing directly to the transmit and receive ring length registers.

The initialization block can not be used if SWSTYLE is 4 or 5. The descriptor ring lengths must be initialized by writing directly to the appropriate registers.

Each ring entry contains the following information:

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62 Am79C976 8/01/00

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To permit the queuing and de-queuing of message buffers, ownership of each buffer is allocated to either the Am79C976 controller or the host. The OWN bit within the descr iptor sta tus informati on, either TM D or RMD, is used for this purpose.

Setting the OWN to 1 signifies that the Am79C976 controller currently has ownership of this r ing descriptor and its associated buffer. Only the owner is permitted to relinquish ownership or to write to any field in the descriptor entry. A device that is not the c ur rent owner o f a descriptor entry cannot assume ownership or change any field in the entry. A device may, however , read from a descriptor that it does not currently own. Software should always read descriptor entr ie s in sequ ential order. When software finds that the curre nt descri ptor is

owned by the Am79C976 controller, then the software must not read ahead to the next descriptor. The software should wai t at a descr iptor it does not own until the Am79C976 controller sets OWN to 0 to release ownership to the software. (When LAPPEN (CSR3, bit

5) is set to 1, this rule is modified. See the LAPPEN description.

At initialization, the base address of the receive descriptor ring is written to CSR24 (lower 16 bits) and CSR25 (upper 16 bits), and the base address of the transmit descriptor ring is written to CSR30 and CSR31.

Figure 28 illustrates the relationship between the initialization base address, the initialization block, the receive and transmit descriptor ring base addresses, the receive and transmit descr iptors, and the recei ve and transmit data buffers, when SSIZE32 is cleared to 0.

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Initialization

Block

IADR[15:0]IADR[31:16]

CSR1

CSR2

TDRA[15:0]

MOD

PADR[15:0] PADR[31:16] PADR[47:32] LADRF[15:0]

LADRF[31:16] LADRF[47:32] LADRF[63:48]

RDRA[15:0]

RLE

RES

RDRA[23:16]

TLE RES

TDRA[23:16]

Rcv

Buffers

RMDO

RMD1

RMD2

RMD3

Rcv Descriptor

Ring

•

1st desc.

2nd desc.

RMD0

Xmt

Buffers

TMD0

TMD1

TMD2

TMD3

Xmt Descriptor

Ring

•

1st desc.

2nd desc.

TMD0

Data

Buffer

Data

Buffer

Data

Buffer

Data

Buffer

Data

Buffer

Data

Buffer

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8/01/00 Am79C976 63

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Note that in this mode the value of CSR2, bit s 15-8, is used as the upper 8-bits for all memory addresses during bus master transfers.

Figure 29 illustrates the relationship between the initialization base address, the initialization block, the receive and transmit descriptor ring base addresses, the receive and transmit descr iptors, and the recei ve and transmit data buffers, when SSIZE32 is set to 1.

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If there is no network cha nnel activity and t here is no pre- or post-receive or pre- or post-transmit activity being performed by the Am79C976 controller, then the Am79C976 controller will periodically poll the current receive and transmit desc riptor entr ies in order to as certain their ownership. If the TXDPOLL bit in CSR4 is set, then the transmit polli ng function is disa bled. The Descriptor Management Unit (DMU) is responsible for these operations.

The Am79C976 controller stores internally the information from two or more receive descriptors and two or more transmit descriptors. Polling operations depend on the ownership of the current a nd next receive and transmit descriptors.

When the poll time has elapsed , if the cu rrent re ceive descriptor is not owned by the Am79C976 controller or if the current rece ive descrip tor is owned a nd the next receive descriptor is not owned, the unowned descr iptor will be polled. Depending on the software style, more than one descriptor may be read in a burst.

If the TXDPOLL bit is not set and the poll time has elapsed, or whenever the TDMD bit is set, if the current transmit descriptor is not owned by the Am79C976 controller, it will be polled. Depending on the software style, more than one descriptor may be read in a burst.

If either transmit or rece ive or both are suspende d or disabled due to the setting of TX_SPND, RX_SPND, SPND, DRX or DTX, the corresponding descriptors will not be polled. Polling is not affected by fast suspend.

Initialization

Block

CSR1CSR2

RMD0

RMD1

RMD2

RMD3

Rcv Descriptor

Ring

•

1st desc.

start

2nd desc. start

RMD0

TMD0

TMD1

TMD2

TMD3

Xmt Descriptor

Ring

•

1st desc.

start

2nd desc. start

TMD0

Data

Buffer

Data

Buffer

Data

Buffer

Data

Buffer

Data

Buffer

Data

Buffer

PADR[31:0]

IADR[31:16] IADR[15:0]

TLE

RES

RLE

RES

MODE

PADR[47:32]

RES

LADRF[31:0]

LADRF[63:32]

RDRA[31:0] TDRA[31:0]

Rcv

Buffers

Xmt

Buffers

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64 Am79C976 8/01/00

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Receive descriptor polling will continue even if transmit polling is disabled by setting TXDPO LL. If at leas t two receive descriptors are owned by the Am79C9 76 controller there will be no descriptor polling if there is no network activity.

The user may change the poll time value from the default value by modifying the value in the Transmit Polling Interval register (CSR47). The default value is 0000h, which corresponds to a polling interval of 65,536 X 3 ERCLK cl ock periods or 2.185 ms when ERCLK = 90 MHz.

When the Am79C976 controller is in the process of receiving a frame and it does not own the next descriptor or if it is in the process of transmitting a frame that does not end in the current descriptor and it does not own the next descriptor, it switches to the chain polling mode in which the polling interval is determined by the Chain Polling Interval register (CSR49). Thus, the device can be programmed to poll at a faster rate when it is abou t to run out of buffers.

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If, after a transmit descriptor access, the Am79C976 controller finds that the OWN bit of that descriptor is not set, the Am79C976 controller resumes the poll time count and re-examines the same descriptor at the next expiration of the poll time count.

If the OWN bit of the descriptor is set, but the Star t of Packet (STP) bit is not set, the Am79C976 controller will immediately request the bus in order to clear the OWN bit of this descriptor. After resetting the OWN bit of this descriptor, the Am79C976 controller will again immediately request the bus in order to access the next descriptor in the ring.

If the OWN bit is set and the buffer length is 0, the OWN bit will be cleared. The Am79C976 controller skips buffers with length of 0, which differs from the C-LANCE device, which interprets a buffer length of 0 to mean a 4096-byte buffer. For the Am79C976 d evice a zero length buffer is acceptable anywhere in the buffer chain.

If the OWN bit and STP are set, the DMA controller will start reading data from the current transmit buffer. If the next transmit descriptor is not al ready known to be owned, the Am79C976 contr ol ler w ill i nterleave a read of this descriptor into the sequence of data DMA operations.

If the next transmit descriptor has the OWN bit set, the Am79C976 cont roller will compl ete reading the d ata from the current transmit buffer, clear the OWN bit in the current descriptor and advance the internal ring pointer to make the next transmit descriptor the new current transmit descriptor.

The Am79C976 contro ller returns owner ship of transmit descriptors to th e software when the DMA transfer of data from system me mory to the Am 79C976 co ntroller’s memory is complete. This is different from older devices in the PCnet family, which will not return the last transmit descriptor of a frame (the one with ENP=1) until transmission of the frame is complete. The Am79C976 controller does not return any status information in the transmit descriptor, it will only write to the OWN bit to clear it.

Normally, the driver will set all the OWN bits of a frame in reverse order so that the Am79C976 controller will never encounter the situation wh ere the cur rent transmit descriptor has OWN=1 and ENP= 0 and the next transmit descriptor has OWN=0. Older devices in the PCnet family treat this condition as a fatal error. The Am79C976 controller allows thi s mode of operation to permit DMA of the beginning of a frame before processing of the entire frame is complete. The number of bytes in the first buffer(s) should be less than the transmit start point or the R EX_UFLO bi t in CMD3 should be set.

When the Am79C976 c ontro ller en counte rs th e condition of the current transmit descriptor’s OWN=1 and ENP=0 and the next transmit descriptor’s OWN=0, it enters the chain pol ling mode. In this mo de, polling of the descriptor will occur at intervals determined by the Chain Polling Interval register (CSR49). Setting the TDMD bit will also cause a poll. Chain polling may be disabled by setting the CHDPOLL bit in CSR7 or CMD2. Note that th is w ill als o di sable chain poll ing for receive descriptors.

If underflow occurs due to delays in setting the OWN bits or excessive bus latency, the transmitter will append an inverted F CS fi el d t o t he frame an d wil l in crement the XmtUnderrunPkts counter. The frame may be retransmitted (if the REX_UFL O bit in CMD3 is set) or discarded.

If an error occurs in the transmission that causes the frame to be discarded (late collision, underflow or retry failure with the corresponding retry or retransmit option not enabled) before the entire frame has been transferred or if the current transmit descr iptor has its KILL bit set, and if current transmit descriptor does not have its ENP bit set, the Am 79C976 c ontr oller wil l skip over the rest of the frame which experienced t he erro r. The Am79C976 controller will clear the OWN bit for all descriptors with OWN = 1 and STP = 0 and continue in like manner until a descr iptor with OWN = 0 (no more transmit frames in the ri ng) or OWN = 1 and STP = 1 (the first buffer of a new frame) is reached.

At the end of any transmit operation, whether successful or with errors, the Am79C9 76 controll er will always perform another polling operation, unless the next transmit descriptor is already known to be owned.

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By default, whenever the DMA controller finishes copying a transmit frame from syste m memor y, it sets the TINT bit of CSR0 to indicate that the buffers are no longer needed. This causes an inter rupt signal if the IENA bit of CSR0 has been set and the TINTM bit of CSR3 is cleared.

The Am79C976 controller provides two modes to reduce the number of transmit int err upts. If the contents of the Delayed Interrupt Register is no t zero, the interrupt to the CPU will be postponed until a programmable number of interrupt events have occurred or a programmable amount of time has elapsed since the first interrupt event occurred. Another mode, which is enabled by setting LTINTEN (CSR5, bit 14) to 1, allows su ppression of interrupts for transmissions of all but the last frame in a sequence.

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If the Am79C976 controller does not own both the current and the next receive descriptor, then the Am79C976 controll er wi ll con tinue to p oll acco rding to the polling seq uence de scr ib ed in the Transmit Polling section. If the receive descriptor ring length is one, then there is no next descriptor to be polled.

If a poll operation has revealed that the current and the next receive descriptors belong to the Am79C976 controller, then additional poll accesses are not necessary. Future poll operations wil l not include r eceive descri ptor accesses as long as the Am79C976 controller retains ownership of the current and the next receive descriptors.

When receive activity is prese nt on the channel, the Am79C976 controller waits until the number of bytes specified in the RCV_PROTECT register (default 64) have been received. If the frame is accepted based on all active addressing schemes at that time, the DMU is notified that a frame has been received.

As receive buffers become available in system memory, the DMA controller will copy frame data from the receive FIFO into system memory. The Am79C976 controller will set t he S T P bit in the firs t des c r iptor of a frame. If the frame length exceeds the length of the current buffer, the Am79C976 controller will pa ss ownership back to the system by wr itin g 0s to the OWN an d ENP bits of the de scriptor w hen the first buffer is full. This activity continues until the Am79C976 controller recognizes the completion of the frame (the last byte of this receive message h as been removed from the FIFO). The Am79C976 controller will subsequently update the current receive descr iptor with the frame status (message byte count, VLAN info, frame tag, error flags, etc.) and will set the ENP bit to 1. The Am79C976 controller will then advance the inter nal ring pointer to make the next receive descriptor the new current receive descriptor.

When the Am79C976 controller has receive data in the FIFO ready to write to system memory, either at the beginning of a new frame or in the middle of a frame that does not fit in the p revious buffer, and it does not own the current receive descriptor, it will immediately poll it. If the OWN bit is still zero, polling of this descr i pto r will continue at a rate determined by the contents of the CHPOLLINT register (CSR49). Polling will occur immediately if the RDMD bit is set.

If the driver does not provide the Am79C976 controller with a descri ptor in a timely fashion, th e receive FIFO will eventually overflow . Subsequent frames will be discarded and the RcvMissPkts MIB counter will be incremented. Normal r eceive operation wi ll resu me when a descriptor is p rovided to the Am79C976 con tro ller an d sufficient data h as been DMA’ed from the Am79C976 controller’s receive FIFO into the system memory.

When the receive FIFO is empty and the Am79C976 device does not own two descriptors (current and next), the Receive Descr iptor Ring is p olled a t an interval by the contents of the TXPOLLINT register (CSR47). When the Am79C976 device owns two descriptors, the Receive Descriptor Ring is not polled at all.

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Setting LAPPEN (CMD2, bit 2 or CSR3, bit 5) to a 1 modifies the way the controller processes receive descriptors. The Am79C976 controller will use the STP information to deter mine where it should beg in writin g a receive packet’s data. Note that while in this mo de, the Am79C976 controller can write intermediate packet data to buffers whose descriptors do not contain STP bits set to 1. Following th e write to the la st descrip tor used by a packet, the Am79C976 controller will scan through the next descriptor entries to locate the next STP bit that is set to a 1. The Am79C976 controller will begin writing the next packet’s data to the buffer pointed to by that descriptor.

Note that because several descriptors may be allocated by the host for each packet and not all messages may need all of the des criptors t hat are allocate d between descriptor s containing STP = 1, then so me descriptors/buffers may be skipped in the ring. While performing the search for the next STP bit that is set to 1, the Am79C976 controller will advance through the receive descriptor r ing regardless of the state of ownership bits. If any of the entries that a re examined during this search indicate Am79C976 controller ownership of the descript or but also indicate ST P = 0, then the Am79C976 controller will reset the OWN bit to 0 in these entries. If a scanned entry indicates host ownership with STP = 0, then the Am79C976 controller will not alter the entry, b ut will advance to the next entry.

When the STP bit is found to be true, but the descriptor that contains this setting is not owned by the Am79C976 controller, then the Am79C976 controller

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will stop advancing through the r ing entr ies and begi n periodic polling of this entry . When the STP bit is found to be true, and the descri ptor that c ontain s this set ting is owned by the Am79C976 controller, then the Am79C976 controller will stop advancing through the ring entries, store the d es cr i ptor information that it has just read, and wait for the next receive to arrive.

This behavior allows the host software to pre-assign buffer space in such a manner that the header portio n of a receive packet will always be written to a particular memory area, and the data portion of a receive packet will always be written to a separate memory area. The interrupt is generated when the header bytes have been written to the header memory area.

Software Interrupt Timer

The Am79C976 controller is equipped with a software programmable free-running interrupt timer. The timer is constantly running and will generate an interrupt STINT (CSR 7, bit 11) when STINITE (CSR 7, bit 10) is set to

1. After generating the interrupt, the software timer will load the value stored in STVAL and restar t. The timer value STVAL (BCR31, bits 15-0) is inter preted as an unsigned number with a resolutio n of 10.24µs. For instance, a value of 98 (62h) corresponds to 1.0 ms. The default v a lue of STVAL is FFFFh which corresponds to

0.671 seconds. A write to STV AL restarts the timer with the new contents of STVAL.

Media Access Control

The Media Access Contr ol ( MAC) engin e in co rporates the essential pro tocol re qui rements for operation of an Ethernet/IEEE 80 2.3- c om pli ant no de and pr ovid es th e interface between the FIFO subsystem and the MII.

This section desc ribes operation of the MAC engine when operating in half-duplex mode. The operation o f the device in full-duplex mode is descr ibed i n the section titled Full-Duplex O peration.

The MAC engine is fully compliant to Section 4 of IEEE Std 802.3, 1998 Edition.

The MAC engine provides programmable enhanced features designed to min imize host super vision, bus utilization, and pre- or post-message processing. These features include the ability to disable retries after a collision, dynamic FCS generation on a frame-byframe basis, automatic pad fiel d i nsertion and de le tio n to enforce minimum frame size attributes, automatic retransmission withou t reloading the FIFO, and automatic deletion of collision fragments. The MAC also provides a mechanis m for automatically in ser ting, deleting, and modifying IEEE 802.3ac VLAN tags.

The two primary attributes of the MAC engine are:

■

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— Framing (frame boundary delimitation, frame

synchronization)

— Addressing (source and destination address

handling)

— Error detection (physical medium transmission

errors)

■ Media access management — Medium allocation (collision avoidance, except

in full-duplex operation)

— Contention resolution (collision handling, except

in full-duplex operation)

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The MAC engine provides minimum frame size enforcement for transmit and receive frames. When APAD_XMT (CSR 4, bit 11) is set to 1, transmit messages will be pad ded with sufficie nt bytes (containin g 00h) to ensure that the receiving station will observe an information field (destinati on add r ess, sou rce add re ss, length/type, data, and FCS) of 64 bytes. When ASTRP_RCV (CSR4, bit 10) is set to 1, the receiver will automatically strip pad bytes from the received message by observing th e value in the length fiel d and by stripping excess bytes if this value is below the minimum data size (46 bytes). Both features can be independently over-ridden to allow illegally short (less than 64 bytes of frame data) messag es to be transmitted and/or received. The use of this feature reduces bus utilization because the pad bytes are not transferred into or out of main memory.

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The MAC engine will autonomously handle the construction of the transmit frame. Once the transmit FIFO has been filled to the pre determi ned threshold ( set by XMTSP in CSR80) and access to the channel is currently permitted, the MAC engine will commence the 7-byte preamble sequence (10101010 b, where first bit transmitted is a 1). The MAC engine will subs equen tly append the Start Frame Delimiter (SFD) byte (10101011b) followed by the serialized data from the transmit FIFO. Once the data has been transmitted, the MAC engine will append the FCS (most si gnificant bit first) which was computed on the entire data portion of the frame. The data portion of the frame consists of destination address, s ource address, length/ type, and frame data. The user is respo nsible for the correct ordering and content in each of these fields in the frame. The MAC does not use the content in the length/type field unless APAD_XMT (CSR4, bit 11) is set and the data portion of the frame is shorter than 60 bytes.

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The receiver section of the MAC engine will detect the incoming preamble seque nce when the RX_DV signal is activated by the external PHY. The MAC will discard the preamble and begin searchi ng for the SFD except in the case of 100B ASE-T4 , for which there is no preamble. In that case, the SFD will be the first two nibbles received. Once the SFD is detected, all subsequent nibbles are treated as part of the frame. The MAC engine will inspect the length field to ensure minimum frame size, strip unnecessa ry pa d characters (if automatic pad stripping is enabled), and pass the remaining bytes through the receive FIFO to the host. If pad stripping is performed, the MAC engine will also strip the received FCS bytes, although nor mal FCS c omputation and checking will occur. Note that apart from pad stripping, the frame will be passed unmodi fied to the host. If the length field has a value of 46 or greater, all frame bytes including FCS will be passed unmodified to th e receive buffer, regardless of the actual frame length.

If the frame termina tes or suffers a collis ion before 64 bytes of information (after SFD) have been received, the MAC engine will automatically delete the frame from the receive FIFO, without host intervention. The Am79C976 controller has the ability to accept runt packets for diagnostic purposes and proprietary networks.

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The first 6 bytes of in formation afte r SFD wi ll be i nterpreted as the des tination address fi eld. The MAC engine provides facilities for physical (unicast), logical (multicast), and broadcast address reception.

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The MAC engine provides several facilities which count and recover from errors on the medium. In addition, it protects the network from gross error s due to inability of the host to keep pace with the MAC engine activity.

On completion of transmission, the MAC engine updates various counters that are described in the Statistics Counters section. The host CPU can read these counters at any time for networ k management purposes.

The MAC engine also attemp ts to prevent the crea tio n of any network err or due to the in ability of th e host to servic e the MAC engine. Dur ing transm ission, if th e host fails to keep the transmit FIFO filled sufficiently, causing an underflow, the MAC engine will guarantee the message is sent with an invalid FCS, which will cause the receiver to reject the message.

The MAC engine can be programmed to try to transmit the same frame again after a FIFO underflow or excessive collision error.

The status of each rece ive mess age is available in the appropriate R eceive Message Descr iptor (RMD). A ll

received frames ar e passed to t he host regar dless of any error.

During the reception, the FCS is generated on every nibble (including the dribbling bits) coming from the MII, although the internally saved FCS value is only updated on each byte boundary. The MAC engine will ignore an extra nibble at the end of a message, which corresponds to dribbling bits on the network medium. A framing or alignment error is reported to the user if an FCS error is detected and there is an extra nibble in the message. If there is an extra nibble but no FCS error, no framing error is reported.

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The basic requirement for all stations on the network is to provide fairness of channel allocatio n. The IEEE

802.3/Ethernet protocols define a media access mech-

anism which permits all stations to access the channel with equality. Any node can attempt to contend for the channel by waiting for a predetermined time (Inter Packet Gap) after the last activity, before transmitting on the media. The channel is a multidr op communic ations media (with various topologic al configurations permitted), which allows a single station to transmit and all other statio ns to receive. If two nodes simultaneously contend for the channel, their signals will interact causing loss of data, defined as a collision. It is the responsibility of the MAC to attempt to avoid and to recover from collisions.

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The IEEE/ANSI 802.3 standard (ISO/IEC 8802-3 1990) requires that the CSMA/CD MAC monitor the medium for traffic by watching for carrier activity. When carrier is detected, the media i s conside red busy, and the MAC should defer to the existing message.

The ISO 8802-3 (IEEE/ANSI 802.3) standard allows an optional two-part def erral after a receive message.

See ANSI/IEEE Std 802.3-1993 Edition, 4.2.3.2.1:

Note: It is possible for the PLS carrier sense indication to fail to be asserted during a collision on the me di a. If the deference process simply times the inter-Frame gap based on this indication, it is possible for a short interFrame gap to be generated, leading to a potential reception failure of a subsequent frame. To enhance system robustness, the following optional measures, as specified in 4.2.8, are recommended when InterFrame-SpacingPart1 is other than 0:

1. Upon completing a transmission, start timing the interrupted gap, as soon as transmitting and carrier sense are both false.

2. When timing an inter-frame gap following reception, reset the inter-frame ga p ti min g i f car rier sense becomes true during the first 2/3 of the inter-frame gap timing interval. During the final 1/3 of the interval,

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the timer shall not be reset to ens ure fair access to the medium. An initial period shorter than 2/3 of the interval is permissible including 0.

The MAC engine implements the optional r eceive two part deferral algorithm, with an Inter FrameSpacingPart1 (IFS1) time of 60 bit times and a n InterFrameSpacingPart 2 time of 36 bit times.

The Am79C976 controller will perform the two-part deferral algorithm as specified in Clause 4.2.8 of IEEE Std

802.3 (Process Deference). The Inter Packet Gap (IPG) timer will start timing the 96-bi t Inte rFrameSpacing after the receive carrier is deasserted.

During the first part deferral (InterFrameSpacingPart1 IFS1), the Am79C976 controller will defer any pending transmit frame and respond to th e rec ei ve message. If carrier sense or collision is detected during the first part of the gap, the IPG counter wi ll b e cl ear ed to 0 c ontinuously until c arrier sense and collisio n are both deasserted , at which poin t the IPG counter will resume th e 96-bit time count once again. Once the IPG counter reaches the IFS1 count (60- bit times), the Am79 C976 controller will not defer to a recei ve frame if a transmit frame is pending. Instead, when the IPG count reaches 96-bit times, the transmitter will star t transmitting, which will cause a collision. The Am79C976 controller will complete the preamble (64-bit) and jam (32-bit) sequence before ceasing transmission and invoking the random backoff algorithm.

The Am79C976 co ntroller allows th e user to program both the IPG and the first part deferral (InterFrameSpacingPart1 - IF S1) through CSR12 5. The user can change the IPG value from its default of 96-bit times to compensate for delays through the exter nal PHY device. Changing IFS1 will a lter the per iod for which the Am79C976 MAC engine will defer to in comi ng recei ve frames.

CAUTION: Care must be exercised when altering these parameters. Undesirable network activity could result!

This transmit two- part deferral algo rithm is implemented as an option which ca n be disabled using the DXMT2PD bit in CSR3. When DXMT2PD i s set to 1, the IFS1 register is ignored, and the value 0 is used for the Inter FrameSpacingPart1 parameter. However, the IPG value is still valid.

When the Am79C976 device operates in full-duplex mode, the IPG timer starts co unting when TX_EN is de-asserted. CRS is ignored in full-duplex mode.

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During the time period immediately after a transmission has been completed, an external transceiver operating in the 10 Mb/s half-duplex mode should generate an SQE T est signal on the COL pin within 0.6 µs to 1.6 µSs after the transmission ceases. Therefore, when the

Am79C976 controller is operating in half-duplex mode, the IPG counter ignores the COL signal during the first 40-bit times of the inter-packet gap. This 40-bit times is the time period in wh ich the SQ E Test message is expected.

The SQE Test was originally d esign ed to check the integrity of the Colli sion Detection mechanism in dependently of the Transmit and Receive capabilities of the Physical Layer. However, MII-based PHY devices detect collisions by sensin g receptions that occ ur during transmissions, a process that does not require a separate level-sensing collision detection mechanism. Collision detection is ther efore dependent on th e health of the receive channel. Sin ce the Link Monitor functio n checks the health of the receive channel, the SQE test is not very useful for MII-based devices. Therefore, the Am79C976 device does not repor t or count SQE Test failures.

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Collision detection is performed and reported to the MAC engine via the COL input pin. Since the COL signal is not required to be synchronized with TX_CLK, the COL signa l must be asser ted for at least t hree TX_CLK cycles in order to be detected reliably.

If a collision is detected before the complete preamble/ SFD sequence has be en trans mit ted, the MAC engine will complete the preamble/SFD before appe nding the jam sequence. If a collision is detected after the preamble/SFD has been completed, but prior to 512 bits being transmitted, the MAC engine will abort the transmission and append the jam sequence immediately. The jam sequence is a 32-bit all zeros pattern.

The MAC engine will attempt to transmit a frame a total of 16 times (initial attem pt plus 15 retries ) due to normal collisions (th ose wi thin the slo t time). D etection of collision will cause the t ransmi ss io n to be resc hed ule d to a time determin ed by the random ba ckoff algorit hm . If a single retr y was required, the Xm tOneCollision counter will be incremented. If more than one retry was required, the XmtMultipleCollision counter will be incremented. If all 16 attempts experienced collisions, the XmtExcessiveCollision counter will be incremented. After an excessive collision error, if REX_RTRY (CMD3, bit 18) is cleared to 0, the transmit message will be flushed from the FIFO. If the REX_RTRY bit is set to 1, the transmitter will not flush the tran smit me ssage from the FIFO. Inst ead, it wi ll clear th e back-off logic and will restart the transmission process, treating the data in the FIFO as a new frame.

If retries have been disabled by setting the DRTY bit in CSR15, the MAC engine will abandon transmis sion of the frame on detection of the first collision. In this case, XmtExcessiveCollision counter will be incremented, and the transmit message will be flushed from the FIFO.

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If a collision is detected after 512-b it times have been transmitted, the collision is termed a late collision. The MAC engine will abor t the transmissi on, append the jam sequence, and increment the Xm tLateCollision counter. If RTRY_LCOL (CMD3, bit 16) is set to 1, th e retry logic treats late collisions just like normal collisions. However, if the RTRY_LCOL bit is cleared to 0, no retry attempt will be scheduled on detection of a late collision. In this case, the transmit message will be flushed from the FIFO.

The ISO 8802-3 (IEEE/ANS I 802 .3) Stan dard r equ ires use of a “truncated binary exponential backoff” algorithm, which provides a controlled pseudo random mechanism to enforce the collision backoff interval, before retransmission is attempted.

See ANSI/IEEE Std 802.3-1990 Edition, 4.2.3.2.5:

“At the end of enforcing a collision (jam ming), the CSMA/CD s ublayer delays before attemp ting t o retransmit the frame. The delay is an integer multiple of slot time. The number of slot time s to delay before the nth retransmission attempt is chosen as a uniformly distributed random integer r in the range:

0 £ r < 2

where k = min (n,10).”

The Am79C976 controller provides an alternative algorithm, which suspends the counting of the slot time/IPG during the time tha t receive carrier sense is detected . This aids in networks where large numbers of nodes are present, and numerous nodes can be in collision. It effectively accelerates the increa se in the backoff time in busy networks and allows n odes not involved in the collision to access the channel, while the colliding nodes await a reduction in channel activity . Once channel activity is reduced, the nodes resolving the collision time-out their slot time counters as normal.

This modified backoff algorithm is enabled when EMBA (CSR3, bit 3) is set to 1.

Transmit Operation

The transmit operation and features of the A m79C97 6 controller are c ontr olle d by prog ramm ab le op tions . T he Am79C976 controller provides a large transmit FIFO to provide frame buffering for increased system latency, automatic retransmission with no FIFO reload, and automatic transmit padding.

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Automatic transmit features such as retry on colli sion, FCS generation/transmission, and pad field insertion can all be programmed to p rovide f lexibility in the (re- ) transmission of messages.

Disable retry on collision (DRTY) is controlled by the DRTY bit of the Mode register (CSR15) in the initialization block.

Automatic pad field inser tion is controlled by the APAD_XMT bit in CSR4.

The disable FCS generation/transmission feature can be programmed as a static feature or dynamically on a frame-by-frame basis.

REX_RTRY (CMD3, bit 18) and REX_UFLO (CMD3, bit 17) can be programmed to ca use the transm itt er to automatically res tar t the transm ission process i nstead of discarding a frame that experiences an excessive collisions or underflow error. In this case the retransmission will not begin until the entire frame has been loaded into the transmit FIFO. The RTRY_LCOL bit (CMD3, bit 16) c an be programmed either to drop a frame after a late collision or to treat late collisions just like normal collisions.

T r ansmit FIFO Watermark (XMTFW) in CSR80 sets the point at which the controller requests more data from the transmit buffers for the FIFO. A minimum of XMTFW empty spaces mus t be available in the transmit FIFO before the controller wil l request the system bus in order to transfer transmit frame data into the transmit FIFO.

Transmit S tart Point (XMTSP) in CS R80 s ets the point when the transmitter actually attempts to transmit a frame onto the media. A minimum of XMTSP bytes must be written to the transmit FIFO for the current frame before transmission of the c ur rent frame wil l begin. (When automatically padded packets are being sent, it is conceivable that the XMTSP i s not reached when all of the data has been tra nsferred to th e FIFO. In this case, the transmission will begin when all of the frame data has been placed into the transmit FIFO.) The default value of XMTSP is 01b, meaning there has to be 64 bytes in the transmit FIFO to start a transmission.

In order to ensure that collis ions occ urrin g within 5 12bit times from the star t of transmis sion (includin g preamble) will be automatical ly retried w ith no host intervention, the transmit FIFO ensures that data contained within the FIFO will not be overwritten unti l at least 6 4 bytes (512 bits) of pream ble plus addr ess, length , and data fields have been transmitted onto the network without encounter ing a coll ision. If the RE X_RTRY bit or the REX_UFLO bit is s et, the transmit data w ill not be overwritten until the frame has been either transmitted or discarded.

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T ransmit frames can be automatically padded to extend them to 64 data bytes (excluding preamble). This allows the minimum frame size o f 64 bytes (5 12 bit s) for IEEE 802.3/ Ethernet to be gu aranteed with no softw are intervention f rom the host/con trolling process. S etting the APAD_XMT bit in CSR4 enables the automatic padding feature. The pad is placed between the LLC

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70 Am79C976 8/01/00

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data field and FCS field in the IEEE 802 .3 frame. FCS is always added if the frame is padded, regardless of the state of DXMTFCS (CSR15, bit 3) or ADD_FCS (TMD1, bit 29). The tra nsmit frame will be pa dded by bytes with the value of 00H. The default value of APAD_XMT is 0 after H_RESET, which will disable automatic pad generation.

If automatic pad generation is disabled, the software is responsible for insuring that the minimum frame size requirement is met. The hardware can reliably transmit frames ranging in size from 16 to 65536 octets.

It is the responsibility of upper l ayer software to correctly define the actual length/type field contained in

the message to correspond to the total number of LLC Data bytes encapsulated in the frame (length/type field as defined in the IEEE 802.3 standard). The length value contained in th e message is not used by th e Am79C976 controller to compute the actual number of pad bytes to be inserted. The Am79C976 controller will append pad bytes dependen t on the actual number of bits transmitted onto the network. Once the last data byte of the frame has completed, prior to appending the FCS, the Am79C976 controller will check to ensure that 544 bits have been transmitted. If not, pad bytes are added to extend the frame size to this value, and the FCS is then added. See Figure 3030.

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The 544 bit count is derived from the following:

Minimum frame size (excluding preamble/SFD, including FCS) 64 bytes 512 bits

Preamble/SFD size 8 bytes 64 bits FCS size 4 bytes 32 bits

At the point that FCS is to be appended, the transmitted frame should contain:

Preamble/SFD + (Min Frame Size - FCS) 64 + (512-32) = 544 bits

A minimum length transmit frame from the Am79C97 6 controller, therefore, will b e 576 bits, af ter the FCS i s appended.

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Automatic generation and transm ission of FCS for a transmit frame depends on the value of DXMTFCS (CSR15, bit 3). If DXMTFCS is cleared to 0, the transmitter will generate and append th e FCS to the transmitted frame. If the transmitter modifies the frame data because of automatic padding o r VLAN ta g manipulation, the FCS will be appended by the Am79C976 controller regardless of the state of DXMTFCS or ADD_FCS (TMD1, bit 29). Note that the c alculated FCS is transmitted most significant bit first. The default value of DXMTFCS is 0 after H_RESET.

When DXMTFCS is set to 1, the ADD_FCS (TMD1, bit

29) allows the automatic generatio n and transmission

of FCS on a frame-by-frame basis. When DXMTFCS is set to 1, a valid FCS field is appended only to those frames whose TX descriptors have their ADD_FCS bits set to 1. If a frame is split into more than one buffer, the ADD_FCS bit is ignored in all descriptors except for the first.

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The Am79C976 transm itter detec ts the following error conditions and increments the appropriate error counters when they occur :

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Late collision erro rs c an on ly oc cu r whe n th e device is operating in half-duplex mode. Loss of carrier and transmit FIFO underfl ow errors are possible whe n the device is operating in half- or full-duplex mode.

When an error occurs in th e middle of a multi-buffer frame transmission, the appropri ate error counter will be incremented, and the tran smission will be abor ted with an inverted FCS field appended to the frame. The OWN bit(s) in the current and subsequent descriptor(s) will be cleared until the STP (the next frame) is found.

Preamble

1010....1010

SFD

10101011

Destination

Address

Source

Address

Length/

Type

LLC

Data

Pad FCS

Bytes

46 – 1500

Bytes

Bits

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If REX_UFLO (CMD3, bit 7) is set, the transmi tter will not flush the frame data from the transmit FIF O after a transmit FIFO underfl ow error occurs. Instead, it will wait until the entire frame has been copied into the transmit FIFO, and then it will restart the transmissio n process.

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The XmtLossCarrier counter is incremented if transmit is attempted when the LINK_ST AT bit in the ST AT0 register is 0.

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A late collision wi ll be d etecte d whe n the device is o perating in half-duplex mode and a collision condi tion occurs after one slot time (512 bit times) after the transmit process was initiated (first bit of preamble commenced). When it detects a late collision, the Am79C976 controller wil l increment the XmtLateColl ision counter. If RTRY_LCOL (CMD3, bit 16) is cl eared to 0, the controller will abandon the transmit process for that frame, and process the next transmit frame in the ring. If the RTRY_LCOL bit is set to 1, transmission attempts that incur late collisions will be retried up to a maximum of 16 attempts.

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An underflow error occurs when the transmitter runs out of data from the transmit FIFO in the middle of a transmission. When this happens, an inverte d FCS is appended to the frame so that the intended receiver will ignore the frame, and the XmtUnderr un Pk ts cou nter is incremented. If REX_UF LO (CM D3, bi t 17) is set to 1 , the transmitter will then wait until the entire frame has been loaded into the transmit FIFO, and then it will restart the transmi ssion of the same frame. If the REX_UFLO is cleared to 0, the transmitter will not attempt to retransmit the aborted frame.

Receive Operation

The receive operation and features of the Am79 C976 controller are c ontr olle d by prog ramm ab le op tions . T he Am79C976 controller uses a large receive FIFO to provide frame buffering for increased system latency, automatic flushing of collision fragments (runt packets), automatic receive pad stripping, and a variety of address match options.

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Automatic pad field str ipping is en abled by setting the ASTRP_RCV bit in CSR4. This can provide flexibility in the reception of messages using the IEEE 802.3 frame format.

The device can be programmed to accept all receive frames regardless of destination address by setting the PROM bit in CSR15. Acceptance of unicast and broadcast frames can be individually turned off by setting the

DRCVPA or DRCVBC bits in CSR15. The Physical Address register (CSR12 to CSR14) stores the address that the Am79C976 controller compares to the destination address of the in coming frame for a unicast address match. T he Logical Address F ilter register (CSR8 to CSR11) ser ves as a hash filter for multicast address match.

The point at which the controller will star t to transfer data from the receive FIFO to buffer memory is controlled by the RCVFW bits in CSR80. The default established during H_RESET is 01b, which sets the watermark flag at 64 bytes filled.

For test purposes, the Am79C976 controller can be programmed to accept runt packets of 12 bytes or larger by setting RPA in CSR124.

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The Am79C976 controll er suppor ts three types of address matching: unicast, multicast, and broadcast. The normal address matching procedure can be modified by prog rammin g three bi ts in CSR1 5, the mode register (PROM, DRCVPA, and DRCVBC).

If the first bit received afte r the SFD (the least s ignificant bit of the first byte of the destination address field) is 0, the frame is unicast, which indicates that the frame is meant to be recei ved by a single nod e. If the fir st bi t received is 1, the frame is mult icast, which indicates that the frame is meant to be received by a group of nodes. If the destination addr ess field contains al l 1s, the frame is broadcast, which is a special type of multicast. Frames with the broadcast address in the destination address field are meant to be received by all nodes on the local area network.

When a unic ast frame arr ives at the Am 79C976 controller, the controller will accept the frame if the destination address field of the incoming frame exactly matches the 6-byte station address stored in the Physical Address register s (PADR, CSR12 to CSR14). The byte ordering is such that the first byte re ceived from the network (after the SFD) must match the least significant byte of CSR12 (PADR[7:0]), and the sixth byte received must match the most si gni fi ca nt byte of C SR1 4 (PADR[47:40]).

When DRCVPA (CSR15, bit 13) is set to 1, the Am79C976 controller will not accept unicast frames.

If the incoming frame is multicast, the Am79C976 controller performs a calculation on the contents of the destination address field to determine whether or not to accept the frame. This calculation is explained in the section that descr ibes the Logical Address Fil ter (LADRF).

When all bits of the LADRF registers are 0, no multicast frames are accepted, except for broadcast frames.

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Although broadcast frames are classified as special multicast frames, they are treated differently by the Am79C976 controlle r hardware. B ro adcas t f rames a re always accepted, except when DRCVBC (CSR15, bit

14) is set. DRCVBC overrides a logical address match. If DRCVBC is set to 1, broadcast frames are not accepted even if the Logical Address Filter is programmed in such a way that a Broad cast frame woul d pass the hash filter.

None of the address filtering described ab ove applies when the Am79C976 controll er is operati ng in the promiscuous mode. In the promiscuous mode, all properly formed packets are received, regar dless of the co ntents of their destination address fields. The promiscuous mode overrides the Disable Receive Broadcast bit (DRCVBC bit Am79C976 in the MODE register) and the Disable Receive Physical Address bit (DRCVPA, CSR15, bit 13).

The Am79C976 controll er operates in promiscuous mode when PROM (CSR15, bit 15) is set.

In addition, the Am79C976 controlle r provides the External Address De tection Interface (EADI) to all ow external address filtering. See the External Address Detection Interface section for further details.

The receive descriptor entry RMD1 contain s t hree b its that indicate which method of address matching caused the Am79C97 6 controller to a ccept the frame. Note that these indicator bits are not available when the Am79C976 controller is programmed to use 16-bit structures for the descriptor entries (BCR20, bit 7-0, SWSTYLE is set to 0).

PAM (RMD1, bit 22) is set by the Am79C976 controller when it accepts the rec eived frame due to a match of the frame’s destination address wi th the co nten t of th e physical address register.

LAFM (RMD1, bit 21) is set by the Am79C976 controller when it accepts the received frame based on the value in the logical address filter register.

BAM (RMD1, bit 20) is set by the Am79C976 controller when it ac cepts the received f rame because the frame’s destination address is of the type ’Broadcast’. Only BAM, but not LAFM, will be set when a Broadcast frame is received, even if the Logical Address Filter is programmed in such a way that a Broadcast frame would pass the hash filter.

When the Am79C976 controller operates in promisc uous mode and none of the three match bits is set, it is

an indication that the Am79C976 controller only accepted the frame because it was in promiscuous mode.

When the Am79C976 c ontroller is no t programmed to be in promiscuous mode, but the EADI interface is used and when none of the three match bits is set, it is an indication that the Am79C976 controller only accepted the frame because it was not rejected by driving the EAR

pin LOW during the receive protect time. The length of receive protect period can be programmed in the Receive Protect Register.

See Table 6 for receive address matches.

Table 6. Receive Address Match

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During reception of an IEEE 802.3 frame, the pad field can be stripped automatically. Setting ASTRP_RCV (CSR4, bit 0) to 1 enables the automa tic pa d str ippin g feature. The pad field will be stri pp ed b efore the frame is passed to the FI FO, thus pres erving FIFO sp ace for additional frames. The FCS fie ld will also be stri pped, since it is computed at the transmitting station based on the data and pad field characters, and will be invalid for a receive frame that has had the pad characters stripped.

The number of bytes to be s tripped is calculated f rom the embedded length field (as defined in the ISO 88023 (IEEE/ANSI 802.3) definition) contained in the frame. The length indicates the actual number of LLC data bytes contained in the mes sage. Any received frame which contains a length field less than 46 bytes will have the pad field str ipped ( if AST RP_RCV is se t). Re ceive frames which have a length field of 46 bytes or greater will be passed to the host unmodified.

Figure 31 shows the byte/bit order ing of the received length field for an IEEE 802.3-compatible frame format.

PAM LAFM BAM Comment

000

Frame accepted due to PROM = 1 or no EADI reject

1 0 0 Physical address match

010

Logical address filter match; frame is not of type broadcast

0 0 1 Broadca st fr am e

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Since any valid Ethernet Type field v alue will always be greater than a nor mal IEEE 802.3 Length field (Š46), the Am79C976 controll er will not attem pt to str ip valid Ethernet fr ames . Note that for some network protocols,

the value passed in the Ethernet Ty pe and/or IEEE

802.3 Length field is not compliant with either standard and may cause problems if pad stripping is enabled.

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Reception and che cking of the received FCS is per formed automatically by the Am79C976 controller. Note that if the Automatic Pad Strippi ng feature is enabled, the FCS for padded frames will be verified against the value computed for the incoming bit stream including pad chara cte rs, but the F CS value for a pa dded frame will not be passed to the host. If an FCS error is detected in any frame, the error will be reported in the CRC bit in the Receive Descriptor.

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Exception conditions for frame reception fall into two categories, i.e., those conditions which are the result of normal networ k operation , and tho se which o ccur due to abnormal network and/or host related events.

Normal exception events are caused by collisions, which can distort and truncate received frames. Frames shorter than 64 bytes will, by default, be discarded. These fragment s will be disca rded regardle ss of whether the receive frame was the first (or only) frame in the FIFO or if the r eceive frame was queued behind a previously received message.

There are two control bits that can be used to cause the MAC to override normal behavior and accept all frames that pass addre ss match, regardless o f the frame length. Setting the Runt Packet Accept (RPA) bit (CMD2, bit 19) causes the MAC to accept runt packets when the device is operating in either half- or full-duplex mode. Setting Full-Duplex Runt Packet Accept (FDRPA, CMD2, bit 20) causes the MAC to accept runt packets when the device is operating in full -duplex mode. (When the value of RPA is 1, runt packets are accepted regardless of the duplex mode or the value of FDRPA.) In either case, there is a minimum frame size of 16 bytes. Frames shorter than this may not be accepted, regardless of the value of RPA or FDRPA.

Abnormal network conditions include:

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These error conditions are reported in the corresponding receive descriptors. The RcvFCS Errors, RcvAlignmentErrors, or RcvMissPkts counter is also incremented when one of these events occurs.

Statistics Counters

In order to provide network management information with minimum host CPU overhead, the Am79C976 device automatically maintains a set of 32-bit controller statistics counter s. These counters are mapp ed di-

Preamble

1010....1010

SFD

10101011

Destination

Address

Source

Address

Length

LLC

Data

Pad FCS

Bytes

46 – 1500

Bytes

Bits

Start of Frame

at Time = 0

Increasing Time

Bit

Bit 7Bit

Bit

Most

Significant

Byte

Least

Significant

Byte

1 – 1500

Bytes

45 – 0

Bytes

Page 74

74 Am79C976 8/01/00

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rectly into PCI memory space and can not be accessed indirectly through the RAP and RDP registers.

To simpli fy the us e of so ftware d ebuggers, the c oun ter logic is designed so that the statistics counters can be accessed one, two, or four bytes at a time. When a portion of a statistics counter is read, the en tire 32 bi ts of the counter is loaded into an internal holding register in a single atomic operation. When the CPU reads one or more bytes from the same coun ter, the data are read from the holding r egister rather than fr om the coun ter. The holding register is updated when either a read access is made to a different counter or a byte of the same counter is read for a second time.

Write acc ess to statist ics counters is provided for debugging purposes only. No holding register is u sed for write accesses. Writing one or two bytes at a tim e to a statistics counter while the network is active can cause unpredictable results.

The contents of the entire set of statistics counters can be cleared to zero by setti ng the INIT_M IB bit (CMD3 , bit 25). The counters will be cleared within approximately 55 ERCLK cycles after the INIT_MIB bit is set.

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The receive statistics counters are defined and the Management Informatio n B ase ( MIB ) objects that they support are listed in Table 7.

For these counters, the defini tion of a valid frame depends on the state of the J UMBO and VSIZE bits (CMD3, bits 21 and 20) as follows:

If JUMBO = 1, valid frames are frames that are between 64 and 65536 bytes in length and have a correct FCS value. Frames longer than 65536 bytes may not be handled properly.

If JUMBO = 0 and VSIZE = 0, valid frames are frames that are between 64 and 1518 bytes in length and have a correct FCS value.

If JUMBO = 0 and VSIZE = 1, valid frames are frames that are between 64 and 1522 bytes in length and have a correct FCS value.

In Table 7, the O ffset column gives the offs et with respect to the value stored in the read-only MIB Offset register, which is located at o ffset 28h in the memor y address space allocated to the Am79C976 device. The actual address of a particular counter is the sum of the following quantities:

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Table 7. Receive Statistics Counters

Offset (hex) Receive Counter Name MIB Object Supported Description of Counter/Comments

00 RcvMissPkts

RMON etherStatsDropEv e nts RMON etherHistoryDropEv ent s MIB-II ifInDiscards E-like

dot3StatsInternalMacReceiveErrors

The number of times a rec eive pac ket was dropped due to lac k of resourc es. This is the number of times a packet was dropped due to receive FIFO overflow. This count does not include undersize, oversize, misaligned or bad FCS packets.

04 RcvOcte ts

RMON etherStatsOctets RMON etherHistoryOctets MIB-II IfInOctets

The total number of octets of data received including octets from invalid frames. This does not include the preamble but does include the FCS bits. The RcvOctets counter is incremented whenever the receiver receives an octet.

08 RcvBroadCastPkts

RMON etherStatsBroadcastPk ts RMON etherHistoryBroadcastPkts EXT-MIB-II ifInBroadcastPkts

The total number of valid frames received that are addressed to a broadcast address. This counter does not include errored broadcast packets or valid multicast pack e ts.

0C RcvMultiCastPkts

RMON etherStatsMultic astPkts RMON etherHistoryMulticastPk ts EXT-MIB-II ifInMulticastPkts

The total number of valid frames received that are addressed to a multicast address. This counter does not include errored multicast packets or valid broadca st packets.

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10 RcvUndersizePkts

RMON etherStatsUndersizePkts RMON etherHistoryUndersiz e P kts

The total number of valid frames received that are less than 64 bytes long (inclu ding the FCS) and do not have any error. SFD must be received so that the FCS can be calculated.

14 RcvOversizePkts

RMON etherStatsOv e rsi z e Pkts RMON etherHistoryOvers izePkts E-like MIB dot3StatsFrameToo Longs

The total number of packets received that are greater than 1518 (1522 when VLAN set) bytes long (incl uding the FCS) and do not have an y error. SFD must be received so that the FCS can be calculated.

18 RcvFragments

RMON etherStatsFragments RMON etherHistoryF ragments

The number of packets received that are less than 64 bytes (not including the preamble or SFD ) and hav e either an FCS error or an alignment error.

1C RcvJabbers

RMON etherStatsJa b bers RMON etherHistoryJab be rs

The number of packets received that are greater than 1518 (1522 when VLAN set) bytes long and have either an FCS error or an alignment error.

20 RcvUnicastPk ts MIB-II ifInUcastPkts

The number of valid frames received that are not addressed to a multicast address or a broadcast address . This counter does not include errored unicast packets.

24 RcvAlignmen tErrors E-like MIB dot3StatsAlignme ntErro rs

The number of packets received that are between 64 and 1518 (1522 when VLAN set) bytes (excluding preamble/SFD but including FCS), i nclusive, an d have a bad FCS with non-integral number of bytes.

28 RcvFCSErrors E-like MIB dot3StatsFCSErrors

The total number of packets received that are between 64 and 1518 (1522 when VLAN set) bytes (excluding preambl e/SFD but including FCS), inclusive, and have a bad FCS with an integ ral num ber of b ytes. This counter will also coun t pack ets with a correct FCS if RX_ER occurs when valid carrier RX_DV is present.

2C RcvGoodOctets

RMON hostInOctets RMON hostTimeInOctets

The total number of bytes received by a port. Bytes are 8-bit quantities received after the SFD. This does not include preamble or bytes from erroneous packets, but does include the FCS.

30 RcvMACCtrl 802.3x aMACControlFramesReceived

The total number of valid frames received with a lengthOrType field value equal to 8808h.

34 RcvFlowCtrl

802.3x aPAUSEMACCtrlFramesReceived

The total number of valid frames received with (1) a lengthOrType field v alue equal to 8808h and (2) an opcode equal to 1.

40 RcvPkts6 4Octets RMON etherStatsPkts64Octets

The total number of packets (including error packets) that are 64 bytes long.

44 RcvPkts6 5to1 27 Oc tets RMON etherStatsPkts6 5to 127 O cte ts

The total number of packets (including error packets) that are 65 bytes to 127 bytes long, inclusive.

Offset (hex) Receive Counter Name MIB Object Supported Description of Counter/Comments

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76 Am79C976 8/01/00

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Table 8 describes the statistics counters associated with the transmitter and lists the MIB objects that these counters support.

In this table the Offset colum n gives the offs et wit h respect to the value stored in the read-only MIB Offset register, which is located at offs et 28h in the memor y address space allocated to the Am79C976 device. The

actual address of a particular counter is the sum of the following quantities:

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Table 8. Transmit Statistics Counters

48 RcvPkts1 28to 25 5O cte ts RMON etherStatsPkts128to255Oct ets

The total number of packets (including error packets) that are 128 bytes to 255 bytes long, inclusive.

4C RcvPkts256to511O cte ts RMON etherStatsPkts256to511Octets

The total number of packets (including error packets) that are 256 bytes to 511 bytes long, inclusive.

50 RcvPkts5 12to 10 23O c tets RMON etherStatsPkts512to1023Octets

The total number of packets (including error packets) that are 512 bytes to 1023 bytes long, inclusive

54 RcvPkts1024to1518Octets

RMON etherStatsPkts1024to1518Octets

The total number of packets (including error pack ets) that are 1024 b ytes to 1518 (1522 when VLAN set) bytes long, inclusive.

58 RcvUnsupportedOpcodes

802.3x an UnsupportedOpcodesReceived

The total number of v alid frames rec eived with (1) a lengthOrType field v alue equal to 8808h and (2) an opcode not equal to 1.

5C RcvSymbolErrors

The number of times when valid carrier (CRS) was present and there was at least one occurrence of an invalid data symbol (RX_ER). This counter is incremented only once per v alid ca rrier ev ent (on ce per frame), and if a collision is present, this counter must not be incremented.

Offset (hex) Receive Counter Name MIB Object Supported Description of Counter/Comments

Offset

(hex) Transmit Counter Name MIB Object Supported Description of Counter/Comments

60 XmtUnderrunPkts

RMON etherStatsDropEv e nts RMON etherHistoryDropEv ent s MIB-II ifOutDiscards E-like

dot3StatsInternalMacTranmsitErrors

The number of times a packet was dropped due to transmit FIFO underrun.

64 XmtOctets

RMON etherStatsOctets RMON etherHistoryOctets RMON hostOutOctets RMON hostTimeOutOctets MIB-II IfOutOctets

The total number of octets of data transmitted. This does not include the preamble b ut does in clu de the FCS bi ts. The XmtOctets counter is incremented whenever the transmitter transmits an octet.

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8/01/00 Am79C976 77

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68 XmtPackets

RMON etherStatsPkts RMON etherHistoryPkts RMON hostOutPkts RMON hostTimeOutPkts BRIDGE-MIB dot1dTpPortOutFrames

The number of packets transmitted. This does not include packets transmitted with errors (i.e., collision fragments and partial packets due to transmit FIFO under runs).

6C XmtBroadCastPkts

RMON etherStatsBroadcastPk ts RMON etherHistoryBroadcastPkts RMON hostOutBroadcastPk ts RMON hostTimeOutBroa dc ast P kts EXT-MIB-II ifOutBroadcastPkts

The number of valid frames transmitted that are addressed to a broadcast address. This counter does not include errored broadcast packets or valid multicast packets.

70 XmtMultiCastPkts

RMON etherStatsMultic as tPkts RMON etherHistoryMulticastPk ts RMON hostOutMultic as tPkt s RMON hostTimeOutMulticastPkts EXT-MIB-II ifOutMulticastPkts

The number of valid frames transmitted that are addressed to a multicast address. This counter does not include errored multicast packets or valid broadcast packets.

74 XmtCollisions

RMON etherStatsColli sio ns RMON etherHistoryCollision s

The number of collisions that occur during transmission attempts. Collisions that occur while the device is not transmitting (i.e., receive collisions) are not identifiable and therefore not counted.

78 XmtUnicastPkts MIB-II ifOutUcastPkts

The number of valid frames transmitted that are not addressed to a multicast or a broadcast address. This counter does not include errored unicast packets.

7C Xm tOneCollision E-lik e dot 3Stat sSi ngl eCollisionFra me s

The number of packets successfully transmitted after e x pe riencing one collision.

80 XmtMultipleCollision E-like dot3StatsMultipleCollsionFrames

The number of packets successfully transmitted a fter experiencing more than o ne collision.

84 XmtDeferredTransmit E-lik e dot 3Stat sD eferredTransmissions

The number of packets for which the first transmission attempt on the network is delayed because the medium is busy.

88 XmtLateCollision E-like dot3StatsLateCo lli si ons

The number of late collisions that occur. A late collision is defined as a collision that occurs more than 512 bit times after the transmission starts. The 512- bit interval is measured from the start of preamble.

8C XmtExcessiveDefer

The number of e xcessive def errals that occ ur. An excessive deferral oc curs when a transmission is deferred for more than 3036 byte times in normal mode or 3044 byte tim es in VLAN mode.

90 XmtLossCarrier

The number of transmit atte mpts made w hen the LINK_STAT bit in the STAT0 register is 0.

94 XmtExcessiveCollision E-like dot3StatsExcessiv eC ol lis io ns

The number of packets that are not transmitted becau se the pac ket experienced 16 unsuccessful transmission attempts (the first attempt plus 15 retries).

Offset

(hex) Transmit Counter Name MIB Object Supported Description of Counter/Comments

Page 78

78 Am79C976 8/01/00

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VLAN Support

Virtual Bridged Loc al Area Network (VLAN) tags are defined in IEE E Std 802.3ac-1998 . A VLAN tag is a 4-byte quantity that is inserted between the Source Address field and the Length/T ype field of a basic 802.3 MAC frame. The VLAN tag consis ts of a Length/Type field that contains the value 8100h and a 16-bit Tag Control Information (TCI) field . The TCI field is fur ther

divided into a 3-bit User Priority field, a 1-bit Canonical Format Indicator (CFI), and a 12-bit VLAN Identifier.

A frame that has no VLAN tag is sa id to be unta gged. A frame with a VLAN tag whose VLAN Identifier field contains the value 0 is said to be priority-tagged. A frame with a VLAN tag with a non-zero VLAN Identifier field is said to be VLAN-tagged.

The format of a VLAN-tagged frame is shown in Figure 32.

98 XmtBackPressure

The total number of back pressure collisions generated.

9C XmtFlowCtrl PAUSEMACCtrlFramesTransmitted

The total number of PAUSE packets generated and transmitted by the controller hardware.

A0 XmtPkts64Octet s RMON etherStatsPkts64Octets

The total number of packets (excluding error packets) that are 64 bytes long.

A4 XmtPkts65to127Octe ts RM ON ethe rStat sPk ts6 5to 127 Octe ts

The total number of packets transmitted (excluding erro r pa ckets) that are 65 b y tes to 127 bytes long, inclusive.

A8 XmtPkts128to255Oct ets RMON etherStatsPkts128to255Octets

The total number of packets transmitted (excluding e rror packet s) that are 128 b ytes to 255 bytes long, inclusive.

AC XmtPkts256to511Octets RMON ethe rStatsPkts256to511Octets

The total number of packets transmitted (excluding e rror packet s) that are 256 byte s to 511 bytes long, inclusive.

B0 XmtPkts512to1023Octets RMON etherStatsPkts5 12 to10 23 Oc tet s

The total number of packets transmitted (excluding e rror packet s) that are 512 b ytes to 1023 bytes long, inclusive

B4 XmtPkts1024to1518Octets RMON etherStatsPkts1024to1518Octets

The total number of packets transmitted (excluding error packets) th at a re 1 024 bytes to 1518 (1522 when VLAN set) bytes long, inclusive.

B8 XmtOversizePkts

The total number of packets transmitted (excluding error pa ck ets) that are long er than 1518 (1522 when VLAN set) bytes.

Offset

(hex) Transmit Counter Name MIB Object Supported Description of Counter/Comments

Page 79

8/01/00 Am79C976 79

PRELIMINARY

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The Am79C976 device includes several features that can simplify the processing of IEEE 802.3ac VLANtagged frames.

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While the maximum frame s ize for IEEE 802.3 frames without VLAN tags is 1518 bytes, the maxi mum frame size for VLAN-tagged frames is 1522 bytes. The VLAN frame size bit (VSIZE, CMD3, bit 20) determines the maximum frame size. When VSIZE is set to 1 the maximum frame size is 1522 bytes. Otherwise, the maximum frame size is 1518 bytes.

The maximum frame size is used for determining when to increment the XmtOversizePkts, XmtPkts1024to 1518Octets, XmtExcessiveDefer, RcvPkts1024to1518Octets, and RcvOversizePkts MIB counters.

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The Admit Only VLAN (VLONLY) bit in the Command1 Register can be programmed to reject any frame that is not VLAN-tagged. When VLONLY is set, untagg ed or priority-tag ged frames wi ll be flu shed from t he recei ve FIFO and will not be copie d int o system memory. Only frames with a Length/Type field equal to 8100h and a non-zero VLAN ID field will be received. The VLAN ID field consists of bits [11:0] of the 15th and 16th bytes of the frame.

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When the SWSTYLE field in CSR58 contains the value 4 or 5, VLAN tag infor mation can be pa ssed between the host CPU and the network medium through Transmit or Receive Descriptors. The transmitter can be programmed to inse rt or delete a VLA N tag or to mo dify the TCI field of a VLAN tag. This feature allows VLAN software to co ntrol the VLAN ta g of a frame wi thout modifying data in transmit buffers. The receiver can determine whether a frame is untagged, pr iority-tag ged, or VLAN-tagged, and it can copy the TCI field of the VLAN tag into the Receive Descriptor

The Tag Con tr ol Co mm and ( TCC) is a 2- bit fie ld in th e Transmit Descriptor that determines whether the transmitter will insert, delete, or modify a VLAN tag or transmit the data from the transmit buffers unaltered. The encoding of the TCC field is shown in Table 9.

If the transmitter adds, deletes, or modifies a VLAN tag, it will append a valid FCS field to the frame, regardless of the state of the Dis able Transmit FC S (DXMTFCS) bit in CSR15.

When SWSTYLE is 4 o r 5, th e rec eiv e r examines each incoming frame and writes the frame’s VLAN classifi cation into the T ag Type (TT) field of the Receive Descriptor. If the frame contains a VLAN tag, the receiver will copy the TCI field of tag into the TCI field of the Receive Descriptor. The encoding of the TT field is shown in Table 10.

PREAMBLE

SFD

DESTINATION ADDRESS

SOURCE ADDRESS

LENGTH/TYPE = 8100h

TAG CONTROL INFORMATION

MAC CLIENT LENGTH/TYPE

MAC CLIENT DATA

FRAME CHECK SEQUENCE

7 OCTETS

1 OCTET

6 OCTETS 6 OCTETS

2 OCTETS

42-1500 OCTETS

4 OCTETS

VLAN ID

CANONICAL FMT INDICATOR

USER PRIORITY

111315

Page 80

80 Am79C976 8/01/00

PRELIMINARY

Table 9. VLAN Tag Control Command

Table 10. VLAN Tag Type

Loopback Operation

Loopback is a mode of operation intende d for system diagnostics. In this mode, the tra nsmitter and receiver are both operating at the same time so that the controller receives its own transmissions. The control ler provides two basic types of loopback. In internal loopback mode, the transmitted data is looped back to the receiver inside the controller without actually transmitting any data to the external network. The receiver will move the received data to the next receive buffer, where it can be examined by software. Alternatively, in external loopback mode, data can be transmitted to and received from the external network.

The external loopback through the MII r equires a twostep operation. The exter nal PHY must be plac ed into a loop-back mode by writing to the PHY Access Register. Then the Am79C976 controller must be placed into an external l oopback mode by setting EX LOOP (CMD2, bit 3).

The internal loopback through the MII is controlled by INLOOP (CMD2, bit 4). When set to 1, this bit will cause the inter nal por t ion of the MII data po r t to loo pback on itself. The MII management port (MDC, MDIO) is unaffected by the INLOOP bit.

The internal MII i nterface is mapped in the following way:

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During the internal loopback, the TX_EN and TXD pins will be active. Internal loopback should no t be us ed on a live network because collisions will not be handled correctly. The wire should be disconnected or the PHY isolated before using internal loopback.

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All transmit and receive function programming, such as automatic transmit p adding and re ceive pad stripp ing, operates identically in loopback as in normal operation.

Runt Packet Accept is intern all y en abled r eg a rdless of the state of the RPA bit in CSR124 when any loopback mode is invoked. This is for backwards compatibility with the C-LANCE (Am79C90) software.

The C-LANCE controller and the hal f-dup lex members of the PCnet family of devices place certain restrictions on FCS generation and checking, and on testing multicast address detection. Since the Am79C976 controller has two FCS generators, these restrictions do not apply to the Am79C976 controller. On receive, the Am79C976 control ler provides true FC S status. The descriptor for a frame with an FCS err or will have the FCS bit (R M D1, b i t 27 ) s et t o 1 . T h e FC S g e ne r a t or on the transmit side can still be disabled by setting DXMTFCS (CSR15, bit 3) to 1.

In internal loopback operation, the Am79C976 con troller provides a s pecial mode to test the co llision logi c. When FCOLL (CSR1 5, bit 4) is set to 1, a coll ision is forced during every transmissi on attempt. Thi s will result in a Retry erro r.

Full-Duplex Operation

The Am79C976 contro ller supports ful l-duplex operation on both network inte rfaces. Full-duplex operation allows simultaneous transmit and receive activity on the TXD[3:0] and RXD[3:0] pins of the MII port. Full-duplex operation is enabled by the FDEN bit loc ated i n BCR9 for all ports. Full-duplex operation is also enabled through Auto-Negotiation when DANAS (BCR 32, bit 7) is not enabled on the MII port and the ASEL bit is se t, and both the external PHY and its link par tner are capable of Auto-Negotiation and full-duplex operation.

When operating in full-duplex mode, the following changes to the device operation are made:

The MAC engine changes for full-duplex operation are as follows:

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TCC

(TMD2[17:16]) Action

00 Transmit data in buffer unaltered 01 Delete Tag Header

Insert Tag Header containing TCI

field from descriptor.

Replace TCI field from buf fer with TCI

data from descriptor.

(RMD1[19:18]) Description

00 Reserved 01 Frame is untagged 10 Frame is priority-tagged 11 Frame is VLAN-tagged

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— Transmission is not deferred while receive is

active.

— The IPG counter which governs transmit deferral

during the IPG bet ween back-to-back transmits is star ted when transmit activity for the firs t packet ends, instead of when transmit an d carrier activi ty ends.

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The Am79C976 controller provides bits in each of the LED Status registers (BCR4, B CR5, BCR6, BCR7) to display the Full-Duplex Link Status. If the FDLSE bit (bit

8) is set, a value of 1 will be sent to the associated LEDOUT bit when in Full-Duplex.

Media Independent Interface

The Am79C976 controller fully supp orts the MII according to the IEE E 802.3 s tandard. This Re conciliation Sublayer interface allows a variety of PHYs (100BASE-TX, 100BASE-FX, 100BASE-T4, 100BASE-T2, 10BA SE-T, etc.) to be attached to the Am79C976 MAC engine without futu re upgrade problems. The MII interface is a 4-bit (nibble) wide data path interface that runs at 25 MHz for 100-Mbps networks or

2.5 MHz for 10-Mbps networks. The in terface consis ts of two independent data paths, receive (RXD(3:0)) and transmit (TXD(3:0)), control signals for each data path (RX_ER, RX_DV, TX_EN), network status signals (COL, CRS), clocks (RX_CLK, TX_CL K) for each data path, and a two-wire management interface (MDC and MDIO). See Figure 3333.

The transmit and receive paths in the Am79C976 controller's MAC are independent. The TX_CLK and RX_CLK need not run at the same frequency. TX_CLK can slow down or stop with out affecting receive and

vice versa. It is only necessary to respect the minimum clock high and low time specificatio ns when switching TX_CLK or RX_CLK. This facilitates operation with PHYs that use MII signaling but do not adhere to 802.3 MII specifications.

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The MII transmit clock is generated by the external PHY and is sent to the Am79C976 controller on the TX_CLK input pin. The clock can run at 25 MHz or 2.5 MHz, depending on th e s pe ed of t he network to which the external PHY is attached. The data is a nibble-wide (4 bits) data path, TXD(3:0), from the Am79C9 76 controller to the external PHY and is synchronous with the rising edge of TX_CLK. The transmit process starts when the Am79C976 controll er asserts TX_EN, whic h indicates to the external PHY that the data on TXD(3:0) is valid.

IEEE Std 802.3 provides a mech anism for signalling unrecoverable errors throug h the MII to the exter nal PHY with the TX_ ER ou t p ut pi n. Th e external PHY will respond to this error by generating a TX coding error on the current transmitted frame. The Am79C976 controller does not use t his m ethod of signaling e rror s on th e transmit side. Instead if the Am79C976 controller detects a transmit error, it will invert the FCS to generate an invalid FCS. Since the Am79C976 controller does not implement the TX_ER function, the TX_ER pi n on the external PHY device should be connected to VSS.

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The MII receive clock is also generated by the external PHY and is sent to the Am79C976 controller on the RX_CLK input pin. The clock will be the same frequency as the TX_CLK but will be out of phase and can run at 25 MHz or 2 .5 M Hz, dep end ing on the speed of the network to which the external PHY is attached.

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82 Am79C976 8/01/00

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The receive process starts when RX_DV is asserted. RX_DV must remain asser ted unt il the end of the receive frame. If the external PHY device dete cts errors in the currently received frame, it asserts the RX_ER signal. RX_ER can be used to signal special conditions out of band when RX _DV is not assert ed. Two defined out-of-band conditions for this are the 100BASE-TX signaling of bad Start of Frame Delimiter and the 100BASE-T4 indication of illegal code group before the receiver has synchronized with the incoming data. The Am79C976 controller will not respond to these conditions. All out of band conditions are currently treated as NULL events. Certain in-band non-IEEE 802.3-compliant flow control sequences may cause erratic behavior for the Am79C976 controller. Consult the switch/ bridge/router/hub manual to disable the in-band flow control sequences if they are being used.

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The MII also provides the CRS (Carrier Sense) and COL (Collision Sense) signals that are required for IEEE 802.3 operation. Ca rri er Sens e is us ed to de tect non-idle activity on the network for the purpose of interframe spacing timing in half-duplex mode. Collision Sense is used to indica te that simultaneous tra nsmission has occurred in a half-duplex network.

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The MII provides a two-wire managemen t interface so that the Am79C976 controller can control external PHY devices and receive status from them.

The Am79C976 cont roller offers direct ha rdware support of the exter na l P HY device without s of tware inter vention. The device automatically uses the MII Management Interface to read auto-negotiation information from the external PHY device and configures

the MAC accordingly. The controller al so provides the host CPU indirect access to the external PHY thr ough the MII Control, Address, and Data regis ters (BCR32, 33, 34).

With software su pport the Am79C976 contro ller can support up to 31 external PHYs attached to the MII Management Interface.

Two independent state machines use the MII Management Interface to poll external PHY devices: the Network Port Manager and the Auto-poll State Machine. The Network Port Manager coordinates the auto-negotiation process, while the Auto-poll State Machine interrupts the host CPU when it detects changes in userselected PHY registers.

The Network Port Manager sends a management frame to the default PHY about onc e every 900 ms to determine auto- ne got iati on re su lts an d the cu rrent link status. The Network Port Manager uses the auto-negotiation results to set the MAC’s speed, duplex mode, and flow control ability. Changes detected by the Network Port Manager affect the operation of the MAC and MIB counters. For example, if link failure is detected, the transmitter will increment the XmtLossCarrier counter each time it attempts to transmit a frame.

The Auto-poll State Machine periodically sends management frames to poll the status register of the default PHY device plus up to 5 us er-selected PHY registers and interrupts the host processor if it detects a change in any of these registers. The Auto-poll St ate Machin e does not change the state of the MAC engine.

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The format of an M II M ana gem ent Frame is defined in Clause 22 of IEEE Std 802.3. The start of an MII Man-

RXD(3:0) RX_DV RX_ER RX_CLK

TXD(3:0) TX_EN

Am79C976

MII Interface

COL

CRS

Receive Signals

Transmit Signals

Management Port Signals

Network Status Signals

TX_CLK

MDIO

MDC

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agement Frame is a preamble of 32 ones t hat gua rantees that all of the external PHYs are synchronized on the same interface. (See F igure 3434.) Loss o f synchronization is po ssible due to the hot-plugging capa-

bility of the exposed MII. The preamble can be suppressed as descr ibed below if the external PHY is designed to accept frames with no preamble.

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The preamble (if present) is followed by a sta rt fiel d (ST) and an operation field (OP). The operation field (OP) indicates whether the Am79C976 controller is initiating a read or write operation. This field is followed by the external PHY add ress (PHYAD) and the register address (REGAD). The PHY address of 1Fh is reserved and should not be used.

The register address field is followed by a bus turnaround field. During a read operation, the bus turnaround field is used to determine if the external PHY is responding correctl y to the read request or not. T he Am79C976 controller wi ll tri-state the MDIO for both MDC cycles.

During the second cycl e of a read operat ion, if t he external PHY is sy nchronized to th e Am79C976 cont roller, the external PHY will drive a 0. If the external PHY does not drive a 0, the Am79C976 controller will signal a MREINT (CSR7, bit 9) interrupt, if MREINTE (CSR7, bit 8) is set to a 1. Th is interrupt indic ates that the Am79C976 controller had an MII management frame read error and that the data read is not valid.

During a write acce ss the A m79C976 contr oller dr ives a 1 for the first bit time of the tur naround fie ld and a 0 for the second bit time.

After the Turn Around field comes the da ta f ield. For a write access the Am79C976 controller fills this field with data to be written to the PHY device. For a read access the external PHY device fills this field with data from the selected register.

The last field of the MII Management Frame is an IDLE field that is nec es sa ry to give ample time for drivers to turn off before the next access.

MII management frames transmitted through the MDIO pin are synchronized with the r ising edge of th e Management Data Clock (MDC). The Am79C976 controller

will drive the MDC to 0 and t r i- st ate th e MDIO anytime the MII Management Port is not active.

To help to speed up the r eading an d writ ing of th e MII management frames to the external PHY , the MDC can be sped up to 10 MH z by setting the FMDC bits i n BCR32. The IEEE 802.3 specification requi res use of the 2.5-MHz clock rate, but 5 MHz and 10 MHz are available for the user. The intended applications a re that the 10-MHz clock rate can be used for a single external PHY on an adapter ca rd or motherboard. The 5-MHz clock rate can be used for an exposed MI I with one external PHY attached . The 2 .5-MHz c lock rate is intended to be used when multi ple external PHYs are connected to the MII Management Port or if compliance to the IEEE 802.3u standard is required.

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The host CPU can indirectly rea d and write external PHY registers through the PHY Access Register or, for compatibility with other PCnet family devices, through BCR33 and BCR34.

To write to a PHY register the host CPU puts the register data into the PHY_DATA field of the PHY Access Register, specifies the address of the external PHY device in the PHY_ADDR field and the PHY register number in the PHY_REG_ADDR field, and sets the PHY_WR_CMD bit.

The Am79C976 device provides two types of read access to external PHY registers, blocking and non-blocking. If a blocking read access is used, the device will generate PCI disconnect/retry cycles if the host CPU attempts to read the PHY Access Register while the MII Management Frame is being processed. If a nonblocking read is used, the PHY Access Register can be read at any time, and the PHY_CMD_DONE bit in that register indicates wh ether o r not PHY_ DATA field contains valid data.

Preamble

1111....1111

OP 10 Rd 01 Wr

PHY

Address

Z0 Rd

10 Wr

Data

Bits

Bit

Idle

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84 Am79C976 8/01/00

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To generate a non-blocking read from a PHY register the host CPU specifies the address of the external PHY device in the PHY_ADDR field and the PHY register number in the PHY_REG_ADDR field of the PHY Access Register and sets the PHY_NBLK_RD_CM D bit. The host CPU can then poll the register until the PHY_CMD_DONE bit is 1, or it can wait for the MII Management Command Compl ete Interru pt (MCCINT in the Int0 Register). Wh en the PHY_CMD_DONE bit is 1, the PHY_DATA field contains the data read from the specifie d ext ernal PHY regist er . If an erro r occurs in the read operation, the MII Management Read Error Interrupt (MREINT) bit in the Interrupt0 Register is set, and if the corresponding enable bit is set (MREINTE in the Interrupt Enable Register), the host CPU is interrupted.

To generate a blocking read, the host CPU uses the same procedure as it does for a non-blocking read, except that it sets the PHY_BLK_RD_CMD bit rather than the PHY_NBLK_RD_CMD bi t, and it c an pol l the PHY Access Register until the PHY_CMD_DONE bit is set.

The host CPU must not set both the PHY_BLK_RD_CMD bit and the PHY_NBLK_RD_CMD bit at the same time.

The host CPU must not attempt a second PHY register access until the first access is complete. When the access is complete, the PHY_CMD_DONE bit in the PHY Access Register and the MII Manag ement Command Complete Interrup t (MCCINT) bit in the Interrupt Re gister will be set to 1, and if the corresponding enable bit is set, the host CPU will be inte rrupted. The host can either wait for this interrupt, or it can use some other method to guarantee that it waits for a long enough time. Note that with a 2.5 MHz MDC clock it takes about 27 µs to transmit a management fra me with a preamble. However, if the Auto-Poll or Port Manage r machines are active, there may be a delay in sending a host generated management frame while other frames are sent. Under these conditions, the host should always check for command completion.

For an MII Management Frame transmitted as the result of a host CPU access to the PHY Access Register, preamble suppressi on is controlled by the Pr eamble Suppression bit (PRE_SUP) in the PHY Access Register. If this bit is set to 1 the preamble will be suppressed. Otherwise, the frame will include a preamble. The host CPU should only set the Preamble Suppr ession bit when accessing a register in a PHY device that is known to be able to accept m anagement frames without preambles. For PHY devices that comply with Clause 22 of IEEE Std 802.3, bit 6 of PHY Register 1 is fixed at 1 if the PHY will accept management frames with the preamble suppressed.

MII Management Frames transmitted as the result of a host CPU accesses to the legac y BCR33 and BCR34 registers are always sent with preambles.

See Appendix B, MII Management Registers, for de- scriptions of the standard registers that are found in IEEE 802.3 compatible devices.

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As defined in t he IEEE 802.3 standard, the exter nal PHY attached to the Am79C976 controller’s MII has no way of communicating important timely status information back to the Am79C976 controller. Unless it polls the external PHY’s status register, the Am79C976 controller has no way of knowing that an external PHY has undergone a ch ange in status. Altho ugh it is possible for the host CPU to poll registers in external PHY devices, the Am79C976 controlle r simpli fies th is proce ss by implementing an a utom ati c po lli ng fu nction that periodically polls up to 6 user-selected PHY registers and interrupts the host CP U if th e content s o f any of th ese registers change.

The automatic polling of PHY registers is controlled by six 16-bit Auto-Poll registers, AUTOPOLL0 to AUTOPOLL5. By wr iting to th e Auto-Poll registers, the user can independently define the PHY addresses and register numbers for six external PHY regist ers. The registers are not restricted to a s ingle PHY device. In the Auto-Poll registers there is an enable bit for each of the selected P HY registers. W hen the host CP U sets one of these enable bits, the Auto-Poll logic reads the corresponding PHY register and stores the result in the corresponding Auto-Poll Data Register. (There is one Auto-Poll Data register for each of the six PHY registers.) Thereafter, at each polling interval, the Auto-Poll logic compares the current contents of the selected PHY register with the corresponding Auto-Poll Data Register. If it detects a change, it sets the MII Management Auto-Poll Interrupt (MAPINT) in the Interrupt Register, which causes an interrupt to the host CPU (if that interrupt is enabled).

Note that when the host CPU writes to one of the AutoPoll Registers the contents of the asso ci ate d Auto-Poll Data Register a re considered to be invalid during the next polling cycle so that the next polling cycle updates the appropriate Auto-Poll Data Register without c ausing an interrupt.

When the conte nts of one of the sel ected PHY re gisters changes, the corresponding Auto-Poll Data Register is updated so that another interrupt will occur when the data changes again.

Auto-Poll Register 0 differs from the other Auto-Poll Registers in several ways. The PHY address (AP_PHY0_ADDR) field of this register defines the default PHY address that is used by both the Auto-Poll State Machine and the Network Port Manager. The

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PRELIMINARY

register number field is fixed at 1 (which corresponds to the external PHY status register), and the register is always enabled. This means that if the Auto-Poll State Machine is enabled, it will always poll register 1 of the default PHY and will interrupt the host CPU when it detects a change in that register.

In addition to the PHY address, register number, and enable bit, the Auto-Poll Registers contain two other control bits for each of the 5 user-selected registers. These bits are the Preamble Suppression (AP_PRE_SUP) and Default PHY (AP_DFLT_PHY) bits.

If the Preamble Suppression bit is set, the Auto-Poll sends management frames to the corresponding register with no preamble field. T he host CPU should only set the Preamble Suppress ion bit for registers in PHY devices that are known to be able to accept management frames without preambles. For PHY devices that comply with Clause 22 of IEEE Std 802.3, bit 6 of PHY register 1 is fixed at 1 if the PHY will acc ept management frames with the preamble suppressed.

If the Default PHY bit (AP_DFLT_PHY) is set, the corresponding Preamble Suppression bit and PHY address field are ignored. In this case the Auto-Poll State Machine uses the default PHY address from the AP_PHY0_ADDR field, and suppresses the preamble if the Network Port Manager l ogic ha s determined that the default PHY device accepts management frames with no preamble. If the Network Port Manager logic has not determined that the default PHY devic e accepts management frames with no preamble, the AutoPoll State Machine does not suppress the preamble when accessing the selected register.

The Auto-Poll State Machine is enabled when the AutoPoll External PHY (APEP) bit (CMD3, bit 24) is set to 1. If APEP is cleared to 0, the Auto-Poll machine does not poll any PHY registers regardless of the state of the enable bits in the Auto-Poll registers. The APEP bit has no effect on the Network Port Manager, which may poll the default PHY even when the state of the APEP bit is 0.

The Auto-Poll’s frequency of generating MII management frames can be adjust ed by setting of the APDW bits (BCR32, bits 10-8). The delay can be adjusted from 0 MDC periods to 2048 MDC periods.

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The Am79C976 controlle r is unique in that it does no t require software intervention to control and configure an external PHY attached to t he MII. This feature was included to ensure backwards co mpatibility with existing software drivers. The Am79C976 controller will operate with existing PCnet drivers from revision 2.5 upward (although older drivers will report incorrect statistics for the Am79C976 device). The hea rt of this au-

tomatic configuration system is the Network Port Manager.

The Network Port Manager initiates auto-negotiation in the external PHY when necessary and monitors the results. When auto-negotiation i s comp lete, the Network Port Manager sets up the MAC to be consistent with the negotiated configuration. The Network Port Manager auto-negotiation sequence requires that the external PHY respond to the auto-negotiation request within 4 seconds. Otherwise, system software will be required to properly contro l and configure th e external PHY attached to the MII. After auto negotiation is complete, the Network Port Manager generates MII management frames about once every 900 ms to monitor the status of the external PHY.

The Network Port Manager is enabled when the Disable Port Manager (DISPM) bit (CMD3, bit 14) is cleared to 0.

Auto-Negotiation

The external PHY and its link partner may have one or more of the following capabilities: 100BASE-T4, 100BASE-TX Full-/Half-Duplex, 10BASE-T Full-/HalfDuplex, and MAC Control PAUSE frame processing . During the au to-negotiati on process the t wo PHY devices exchange information about their capabilities and then select the best mode of operation that is common to both devices. The modes of operation are prioritized according to the order shown in T ab le 11 (with the highest priority shown at the top of the table).

T able 11. Auto-Negotiation Capabilities

Auto-Negotiation goes further by providing a messagebased communication scheme called, Next Pages, before connecting to the Link Par tner. The Network Port

Manager does not support this feature. However, the host CPU can disable th e Network Port Ma nager and manage Next Pages by accessing the PHY device through the PHY Access Regis ter. The host CPU can

disable the Network Por t Manager by settin g the Disable Port Manager (DISPM) b it (CMD3, bit 14) to 1. (The DISPM bit corresponds to the Disable Auto-Negotiation Auto Setup (DANAS) bit in BCR32 of older PCnet family devices.)

Network Speed Physical Network Type

200 Mbps 100BASE-X, Full Duplex 100 Mbps 100BASE-T4, Half Duplex 100 Mbps 100BASE-X, Half Duplex

20 Mbps 10BASE-T, Full Duplex 10 Mbps 10BASE-T, Half Duplex

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86 Am79C976 8/01/00

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To control the auto-negotiation process, the Network Port Manager generates MII Management Frames to execute the procedure descr ibed below. (See Appen- dix B, MII Management R egisters, for the MII register bit descriptions.)

The Network Port Manager is held in the IDLE stat e while H_RESET is asser ted, while the EEPROM is being read and while the DISPM bit is set. When non e of these conditions are true, the Network Port Manager proceeds through the following steps:

1. If XPHYRST is set, write to the PHY’s Control Reg- ister (R0) to set the Soft Reset bit and cause the PHY to reset. The Network Port Manager then periodically reads the PHY’s Control Register (R0) until the reset is complete.

2. If XPHYRST is not set or after the PHY reset is complete, the PHY’s Status Register (R1) is read.

3. If the PHY’s Auto-Negotiation Ability bit (R1, bit 3) is 0 or if the XPHYANE bit in the Control2 Register is 0, write to the PHY’s Control Register (R0) to disable auto-negotiation and set the speed and duplex mode to the values specified by the XPHYSP and XPHYFD bits in the Control2 Reg ister “and”ed with the appropriate bits from the PHY's Technology Ability Field. Then proceed to step 8.

4. Otherwise write t o the Auto-Negotiation Adver tisement Register (R4). Bits A0 to A5 of Technology Ability field of R4 are taken from bits 15 to 11 in R1. Bit A6 of the Technology Ability field indicates the MAC's ability to respond to MAC Control Pause frames. This bit is set equal to the value of the Negotiate Pause Ability (NPA) bit in the Flow Control Register. The Next Page, Acknowledge, and Remote Fault bits are set to 0, and the Se lector Field is set to 00001 to indicate IEEE Std 802.3.

5. Write to the Control Register (R0) to restart Autonegotiation.

6. Poll R1 until the Auto-Negotiation Complete bit is set to 1.

7. Read the Auto-Negotiation Link Partner Ability Register (R5). Set the MAC's speed, duplex mode, and pause ability to the highest pr iority mode that is common to both PHY devices.

8. Poll R1 until the Link Status bit is 1. If Link Status is not found to be 1 after two polls at 900 ms intervals, go back to step 1.

9. Poll R1 at intervals of about 900 ms until the Link Status bit is 0. Go to step 8.

When Auto-Negotiation is comp lete, the Network Port Manager examines the MF Preamble Suppre ssion bit in PHY register 1. If this bit is set, the Network Port Manager suppresses preambles on all frames that i t sends until one of the following events occurs:

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A complete bit description of the MII and AutoNegotiation registers can be found in Appendix B.

The Network Port Manager is not di sabled when the MDIO pin is held low when the M II M ana gement Interface is idle. If no PHY is connected, reads of the external PHY's registers will result in read errors, causing the MREINT interrupt to be asserted.

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The MII Management Inter face (MDC and MDIO) can be used to manage more than one external PHY device. The external PHY devices may or may not be connected to the A m79C976 controller’s MII bus. For example, two PHY devices ca n be connected to the Am79C976 controller’s MII bus so that the MAC can communicate over either a twisted-pair cable or a fiberoptic link. Conversely, several Am79C976 controllers may shar e a si ng l e int egrated circ ui t th at co nta in s several PHY devices with separate MII busses but with only one MII M anagement bus. In th is case, the MII Management Interface of one Am79C976 controller could be used to manage PHY devices connected to different Am79C976 controllers.

If more than one PHY device is connected to the MII bus, only one PHY device is allowed to be enabled at any one time. Since the Network Port Manager can not detect the presen ce o f mor e tha n one PHY on the M II bus, the host CPU is responsible for making sure that only one PHY is enabled. The host CPU can use the PHY Access Register to s et the Isolat e bit in the Control Register (Register 0, bit 10) of any PHY that needs to be disabled.

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The Port Manager normally sets u p the sp eed, du plex mode, and flow control (pause) ability of the MAC based on the results of auto-negotiation. However, it is possible to operate the Am79C976 d evice with no MII Management Interface connection, in which case the Port Manager is n ot able to star t the auto-neg otiation process or set up the MAC-based on auto-n egotiation results. This may happen if the Am79C976 controller is connected to a multi-PHY device that has only one MII Management Interface that is shared among s everal PHYs.

If the Am79C976 controller is operating without a MII Management Interface conne ction to it s externa l PHY, the host CPU can force the MAC into the desired state by setting the DISPM bit in CMD3 Register to 1 to disable the Port Manager, then writing to the following bits:

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PRELIMINARY

1. FORCE_FD (CMD3, bit 12),

2. FORCE_SPEED (CTRL2, bits 18-16),

3. FORCE_LINK_STAT (CMD3, bit 11), and

4. Force Pause Ability (FPA, FLOW_CONTROL, bit

20).

These bits set up the duplex mode, speed, a nd flow control ability in the MAC and put the MAC into the Link Pass sta te.

Regulating Network Traffic

The Am79C976 device provides two hardware mechanisms for regulating ne twork traffic: 802. 3x Flow Control and collision-based back pressure. 802.3x Flow Control applies to full-duplex operation only, while back pressure applies to ha lf-duplex operation only. 802.3x Flow Control wor ks by sending an d receiving MAC Control PAUSE frames, which cause the receiving station to postpone transmissions for a time determined by the contents of the P A USE frame. Back pressure forces collisions to oc cur when other no des attem pt to transmit, thereby preventing other nodes from transmitting for periods of times determined by the back-off algorithm.

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The format of a MAC Control Pause frame is s hown i n Table 12.

When a network station th at supports IEEE 80 2.3x Flow Control receives a pause frame, it must suspen d transmissions after the end of any frame that was being transmitted when the p ause frame a rrived. The length of time for which the station must suspend transmissions is given in the request_operand field of the pause frame. This pause time is given in units of slot times. For 10-Mbps and 100- Mbps 802.3 net works, one slot time is 512 bit tim es. The request_ope rand field is in-

terpreted as Big-Endian data--octet 17 is the most significant byte and octet 18 is the least significant byte.

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The Am79C976 device supports collision-based back pressure for congestion co ntr ol whe n th e device is operating in half-duplex mode. Back pressur e is enabled when the device is operating in half duplex mode and either the Flow Control Command bit (FCCMD, FLOW_CONTROL, bit 16) is set or the FC Pin E nable bit (FCPEN, FLOW_CONTROL, bit 17) is set and th e FC pin is asserted.

When the MAC begins r eceiving a frame that passes the address matching criteria and if back pressure is enabled, the MAC will intentionally cause a collision by transmitting a “phantom” frame consisting of a continuous stream of altern ating 1s and 0s. Th e length of the phantom frame is 568 bits so that it will be inter preted as a runt frame.

Back pressure does not affect the transmission of a frame. The MAC will only force a co llision when it begins to receive a new frame.

The generation of a Back-Pressure collision causes the XmtBackPressure MIB Counter to increment.

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Traffic regulation can be controlled either by external hardware or by CPU commands. Tr affic regulation is affected by the following:

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The duplex mode affects the type of traffic regulation that is used. In f ull-duplex mode the FC pi n and the FCPEN, FCCMD, and FIXP bits control the transmission of pause frames. In half-duplex mode the same pin and bits control the assertion of back pressure. Also, in half-duplex mode th e Am79C976 device does not respond to received pause frames.

The Am79C976 device includes support for two styles of full-duplex flow control. In one style, which is similar to an XON-XOFF protocol, a pause frame whose request_operand field (bytes 17 and 18) contains 0FFFFh is sent to prevent the link partner from transmitting. Later, a pause fram e whose request_operand field contains 0 is sent to allow the link partner to resume transmissions. This style of flow control is selected by clearing the Fixed Length Pause bit (FIXP) to 0.

Table 12. MAC Control Pause Frame Format

Octet

Numbers Field Name Value

1-6

Destination Address

01-80-C2-00-00-01

7-12 Source Address

Sender’s physical address

13-14 Length/Type 88-08

15-16

MAC Control Opcode

00-01

17-18 Request_operand

Pause time measured in

slot times 19-60 Pad Zeros 61-64 FCS FCS

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88 Am79C976 8/01/00

PRELIMINARY

For the other style of flow control, a single pause frame is sent to halt transmissions for a predetermined period of time. The contents of the request_operand field of this frame are taken from the Pause Length register. This style of flo w control is se lected by set ting the Fix ed Length Pause bit (FIXP) to 1.

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The Flow Control pin (FC) allows external hardware to cause pause frames to be transmitted or back pressure to be asserted. The use of the FC pin for traffic regulation is enabled by the FC Pin Enable bit (ENFC). When FCPEN is cleared to 0, the signa l on the FC pin is ignored. Otherwise, back pressure is enabled when FC is high and the device is operating in half-duplex mode, and pause frames are sent at FC pin signal transitions when the device is operating in full-duplex mode.

In full-duplex mode with the FC Pin Enable bit (FCPEN) =1, the actions that occur at low-to-high and high-tolow transitions of the FC pin depend on the value of the Fixed Length Pause bit (FIX P). If FIXP is 1 , a low-tohigh transition causes a pause frame to be sent with its request_operand field contents taken from the Pause Length regist er. In this case high-t o-low transition s of the FC pin are ignored.

If FIXP is 0, a low-to-high transition sends a pause frame whose request_operand field contains 0FFFFh , while a high-to-low transition sends a pause frame whose request_operand field contai ns 0.

The effects of the FC pin are summarized in Table 13.

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For software control of traffic r egula tion th e Fl ow Control Command bit (FCCMD) mimics the FC pin.

In half-duplex mode, back pressure is enabled when FCCMD is set to 1, an d it i s disabled w hen FCCMD is cleared to 0.

In full-duplex mode, the act of se tting FCCMD to 1 causes a pause frame to be se nt. The con tents of th e request_operand field of the frame depend on the state of the FIXP bit. If FIXP is 1, the contents of the request_operand field are copied from the Pause Length register. If FIXP is 0, the contents of the request_operand field are set to 0FFFFh.

In full-duplex mode, if FIXP is 0, the act of clearing FCCMD to 0 causes a pause frame to be sent with its request_operand field cleared to 0.

If FIXP is set to 1, the FCCMD bit is self-clearing--the CPU does not have to write to the Am79C976 device to clear the FCCMD bit. This allows the CPU to use a single write access to cause a pause frame to be sent with a predetermined re que st_ ope rand field.

Table 13. FC Pin Functions

FC Pin

Transition FCPEN FIXP

Duplex

Mode Action

X 0 X X No Action

0 to 1 1 X Half

Enable back pressure

1 to 0 1 X Half

Disable back pressure

0 to 1 1 1 Full

Send pause frame with request operand equal to the contents of the Pause Length register

1 to 0 1 1 Full No action

0 to 1 1 0 Full

Send pause frame with request operand equal to 0FFFFh.

1 to 0 1 0 Full

Send pause frame with request operand equal to 0000h.

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8/01/00 Am79C976 89

PRELIMINARY

The effects of the FCCMD bit are summarized in Table 14.

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When the host CPU changes the contents of the Pause Length Register, it must make sure that no Pause frame is transmitted while the register is being updated. If the host CPU can not control the state of the FC pin, it can clear the FCPEN pin so that the FC pin will be ignored. It can then poll the PAUSE_PENDING bit in the Status0 Register until that bit is 0. Wh en FCPEN and PAUSE_PENDING are bot h 0, it i s safe to writ e to the Pause Length Register.

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The ability to respond to received pause frames, or pause ability, is controlled independently from the transmission of pause frames. When pause ability is enabled, the receipt of a pause frame caus es the device to stop transmitting for a time peri od that is determined by the contents of the pause frame.

Pause ability is enabled by Negotiate Pause Ability (NPA, FLOW_CONTROL, bit 19) and Force Pause Ability (FPA, FLOW_CONTROL, bit 20). If the FPA bit is set, pause ability is enabled regardless of the Pause Ability state of the link partner. If the NPA bit is set and the FP A bit is not set, pause ability is enabled only if the auto-negotiation proc ess dete rmines that the link partner also supports 802.3x flow control.

The auto-polling state machine is extended to read the external PHY Status registers at register locations 1, 4, and 5. (The contents of these register s are defined i n

the IEEE P802.3u specification.) From Register 1 the state machine obtains the link status and auto-negotiation status as well as Jabber and Remote Fault indications. If auto negotiation is complete, the logic uses the T echnolog y Ability fields of the Auto-Negotiation Advertisement register (Register 4) and the Auto-Negotiation Link Partner Ability register (Register 5) to determine the network speed and duplex mode and the flow control status. The MAC device will be put into the speed and duplex mode for the highest common ability that the PHY and its link partner share. If full-duplex mode is selected and the PAUSE bits are set in both Register 4 and Register 5, pause ability wil l be enabled so that the MAC will be able to respond to MAC Control P A USE frames as de scribed in the I EEE P802. 3x specif icatio n.

A MAC Control PAUSE frame is any valid frame with the following:

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If such a frame is received while pause ability is enabled, the MAC device will wait until the end of the frame currently being transmitted (if any) and then stop transmitting for a time equal to the value of the request_operand field (octets 17 a nd 18) multip lied by 512-bit times.

If another MAC Control PAUSE frame is received before the Pause timer has timed out, the Pause timer will be reloaded from th e request_operand field of the new frame so that the new frame overrides the earlier one.

Received MAC Control PAUSE frames are handle d completely by the Am79C976 hardware. They are not passed on to the host co mputer. However, MAC Control frames with opcodes not equal to 0001h are treated as normal frames, except that their reception causes the Unsupported Opcodes counter to be incremented.

Since the host computer does not receive MAC Control PAUSE frames, 32-bit MIB counters have been added to record the following:

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Delayed Interrupts

To reduce the host CPU interrupt service overhead the Am79C976 device can be programmed to postpone the interrupt to the host CPU until either a programmable number of receive or transmit interrupt events have occurred or a programma ble amount of time has

Table 14. FCCMD Bit Functions

FCCMD

Transition FIXP

Duplex

Mode Action

0 to 1 X Half Enable back pressure 1 to 0 X Half Disable back pressure

0 to 1 1 Full

Send pause frame with request operand equal to the contents of the P ause Length register. Automatically clear FCCMD to 0.

1 to 0 1 Full

No action. (FCCMD is cleared automatical ly when FIXP = 1.)

0 to 1 0 Full

Send pause frame with request operand equal to 0FFFFh.

1 to 0 0 Full

Send pause frame with request operand equal to 0000h.

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90 Am79C976 8/01/00

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elapsed since the first inter rupt event occurred. Th e use of the Delayed Interrupt Register allows the interrupt service routine to process several events at one time without having to retur n control back to the operating system between events.

A receive interrupt event occurs when receive interrupts are enabled, and the Am79C976 device has completed the reception of a frame and has updated the frame’s descriptors. A receive interrupt event causes the Receive Interrupt (RINT) b it in CSR0 to be se t if it is not already set. Similarly, a transmit interrupt event occurs when transmit interrupts are enabled, and the Am79C976 device has cop ied a transmit frame ’s data to the transmit FIFO and has u pdated the f rame’s descriptors. A transmit interr upt event causes the Transmit Interrupt (TINT) bit in CSR0 to be set if it is not already set. No te that frame rec eptions or transm issions affect the interrupt event counter only when receive or transmit interrupts are enabled.

The Delayed Interrupt Register contains the 5-bit Event Count field and the 11-bit Maximum Delay Time field.

Each time the hos t CPU clears the R INT or TINT bit , the contents of the Event Count field are loaded into an internal interr upt event counter, the contents of the Maximum Delay Time field are load ed into an int ernal interrupt event timer, and the interrupt event timer is disabled. Each time a receive or transmit interrupt event occurs, the interrupt event counter is decremented by 1 and the interrupt event timer is enabled, or if it has already been enabled, it continues to count down. Once the inter rupt event timer has been enabled, it decrements by 1 every 10 microseconds.

When either the interrupt event counter or the interrupt event timer reaches zero, the INTA

pin is asserted.

External Address Detection Interface

The EADI is provided to allow external address filtering and to provide a Receive Frame Tag word for proprietary routing information. This feature is typically utilized by terminal servers, switches and/or router products. The EADI inter face can be used in conjunction with external logic to capture the packet destination address from the MII inp ut data stre am as it arr ives at the Am79C976 controller, to compare the captured address with a table of stored add resses or identifiers, and then to deter mine whether or not the Am79C97 6 controller should accept the packet.

The EADI consists of the External Address Reject (EAR

), Start Frame-Byte Delimiter (SFBD), Receive Frame Tag Data (RXFRTGD), and Receive Frame Tag Enable (RXFRTGE) pin s.

The SFBD pin indicates two types of information to the external logic--the start of the frame and byte boundaries. The first low-to-high transition on the SFBD pin

after the asser tion of the RX_DV signal indicates that the first nibble of the Destination Address field of the incoming frame is available on the RXD[3:0] pins. Thereafter, SFBD toggles with each RX_CLK pulse so that SFBD is high when the least significant nibble of frame date is present on the RXD[3:0] lines and low when the most significant nibble is present. SFBD stays low when RX_DV is not asserted (which indicates that the receiver is idle).

Note that the SFBD signal is available on any LED pin. To direct th e SFBD signal to one of the LED pins, the SFBDE and LEDPOL bits should be set to 1 and the PSE bit should be c leared to 0 in th e appr opr iate LE D register. The SFBDE bit directs the SFBD signal to the pin, the LEDPOL bit sets the polarity to active high and enables the totem-pole driver, and the PSE bit disables the LED pulse stretcher logic.

If the system needs all four LEDs as wel l as the EA DI function, the Am79C976 controller can be programmed to use the shared pin for the LED function, and the external logic can be designed to generate the SFBD signal by searching for the 1101 0101b Start Frame Delimiter (SFD) pattern in the RCD[3:0] data.

The external addre ss dete ction l ogi c can use the EAR input to indicate whether or not the incoming frame should be accepted. If the EAR

signal remains high during the receive protect time, the frame will be accepted and copied into host system memory. The receive protect time is a period of time measured from the receipt of the SFD field of a frame. The length of the receive protect time is programmable through the Receive Protect Register.

A frame is accepted if it passes eit her the inter nal address match criteria or the external add ress matc h criteria. If th e internal addr ess logic is disabled, the acceptance of a frame depends entirely on the external address match logic. If the external address match logic is disabled, the acceptance of a frame depends entirely on the internal address match logic.

Internal address match is disabled when PROM (CSR15, bit 15) is cleared to 0, DRCVBC (CSR15, bit

14) and DRCVPA (CSR15, bit 13) are set to 1, and the Logical Address Fil ter registers ( CSR8 to CSR11) are programmed to all zeros.

External addr es s m atc hin g ca n be di s abled by holdin g the EAR

pin low. There is no programmable bit that causes the Am79C976 device to ignore the state of the EAR

pin.

The EADI logic only samples EAR

from 2 nibble times after SFD until the end of the receive protect time. (See the Receive Protect Register section.) The frame will be accepted if EAR

has not been asse r ted dur ing this

window . EAR

must have a pulse width of at least two bit

times plus 10 ns.

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8/01/00 Am79C976 91

PRELIMINARY

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Receive Frame Tagging is a feature that allows the external addres s detecti on logic to pas s an identi ficatio n code or tag to the Am79C976 controller to be placed in the RX descrip tor correspondi ng to a received frame. The external logic can shift this tag in as a serial bit stream on the Receive Frame Tag Data (RXFRTGD) pin. It uses the Receive Frame Tag Enable (RXFRTGE) pin to indicate when the tag data is valid. The clock signal for shifting in the tag data is RX_CLK. See Figure 3535.

If the Software Style (SWSTYLE) fie ld in BCR20 contains the value 2 or 3, the Receive Frame Ta g can be up to 15 bits long. I n thi s ca se the tag data is s amp le d on the low-to-high transition of RX_CLK whenever RXFRTGE is high. If SWSTLYE = 5, the Receive Frame Tag can be up to 32 bits long. In this case, the tag data is sampled on both edges of RX_CLK so that the entire tag can be shifted in 16 RX_CLK cycles or less, depending on the length of the tag. If SWSTYLE is 0 or 4, Receive Frame Tagging is not s upported. In those cases the descr iptor space is allocated to ot her functions.

If SWSTYLE = 5, t ag bits are s hifted in the order B31 , B15, B30, B14, … , B0, where B0 is the least significant bit of the tag. This sequence allows t he external log ic to be simplified slightly if the system design requir es a

frame tag of fewer than 17 bits. In this case the external logic can use only one clo ck edge to shift in the data. Since the Am79C976 device samples the RXFRTGD pin on both edges of RX_ CLK, the same data will appear in the upper and lower halves of the frame tag field in the descriptor.

If SWSTYLE = 2 or 3, tag bits are shifted i n the order B14, B13, ... , B0.

Because of the order in which frame tag bits are shifted in, if the tag is shorte r tha n 15 bits, the tag data will be placed in the least signif icant porti on of the Receive Frame Tag field of the RX descriptor, and the most significant bits of the field will be cleared to zeros.

RXFRTGE need not be a continuous signal. It can toggle on and off so that the tag data can be shifted in at a slower rate than the frequency of RX_CLK. The length of the frame tag i s determined by the numb er of RX_CLK cycles during which RXFRTGE is asserted before the end of the frame arrives (with a maximum of 15 bits for SWSTYLE 2 or 3 or a maximum of 32 bits for SWSTYLE 5). The last bit of the Receive Frame Tag must be shifted into the RXFRTGD input at least one RX_CLK cycle before RX_DV is de-asserted.

The Receive Frame Tagging feature is enabled by the RXFRTAGEN bit in the Command1 Register. When this bit is cleared to 0, the Receive Frame Tag field of th e RX descriptor will be filled with zeros.

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External Memory Interface

The Am79C976 controll er contains an Exter nal Memory Interface that suppor t s Flash (or EP ROM) devices as boot devices, as well as SSRAM for frame data storage. The controller pr ovides read and wr ite access t o Flash or EPROM. No glue logic is required for the memory interface.

The Am79C976 device contains a built-in self test system (MBIST) that can be programmed to run a diagnostics test on the external SSRAM.

The external SSRAM is organized around a 32-bit data bus. The memory can be as large as 1M X 32 bits. The memory devices can be either JEDEC sta ndard Pipeline Burst Synchronous Static RAM devices (PB-SSRAM) or ZBT™ Synchronous Static RAM (ZBTSSRAM) with pipelined outputs. The SRAM_TYPE field of the Control1 Register must be initialized to indicate which type of SSRAM is actually used.

RX_CLK

RX_DV

MIIRXFRTGE

MIIRXFRTGD

SF/BD

Page 92

92 Am79C976 8/01/00

PRELIMINARY

The contents of the SRAM_TYPE fi eld are defin ed in Table 15.

The width of the Flash memor y (or EPROM) is 8 bits. The memory can be as large as 16M X 8 bits.

The external memory bus uses the same address, data, and control pins to access both Flash and SSRAM memory, but it has separate chip select (or chip enable) pins so that only one device can be selected at a time. FLCS

selects the Flas h memory, while

ERCE

selects the SSRAM. The Flash memor y must not be accessed when the Am79C976 controller is running (when the RUN bit in CMD0 is set to 1) . Any access to the Flash memory clears the RUN bit and

thereby abruptly stops all network and DMA operations.

ERA[19:0] provides 20 bits of address for the SSRAM and the lower 20 bits of address for the Flash memory. The higher 4 bits o f ad dr es s for the Fla sh me mory are shared with bits [11:8] of the SSRAM data bus (ERD[11:8]). The lower 8 bits of th e external memor y data bus ERD[7:0] are us ed by both the SSRAM an d the Flash. The high order 20 bits of the external memory data bus ERD[31:12] are used only by the SSRAM.

The output enable signal for the Flash (FLOE

) shares a

pin with the SSRAM Address Advance signal (ERADV). Figure 36 shows how the SSRAM and Flash can be

connected to the Am79C976 controller.

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The Am79C976 controller supports EPROM or Flash as an Expansion ROM boo t device. Both are configured using the same me thods and operate the same. See Figure 3636. Se e the previous secti on on Expansion ROM transfers for the PCI timing and functional description of the transfer method.

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Table 15. SRAM_TYPE Field Encoding

SRAM_TYPE[1:0] External Memory Type

00 Reserved 01 ZBT 10 Reserved 11 Pipelined Burst

ERCLK

EROE

A[19:0] DQ[7:0]

OE CS

L4 Controller

FLASH

A[23:20]

SSRAM

CLK A[16:0] CE1 OR CE2 D[31:0] OE GW OR R/W

ADV ADSP OR CEN CE

ERA[19:0]

ERD[31:0]

ERWE/FLWE

ERADV/FLOE

ERADSP/CEN

ERCE

FLCS

1720

[11:8]

[7:0]

A17

Page 93

8/01/00 Am79C976 93

PRELIMINARY

The Am79C976 controller will always read four bytes for every host Expansion ROM read access. The interface to the Expansion Bus is timed by an internal signal called ROMCLK, which runs at one fourth of the frequency of the external memory interface clock (ERCLK). Thus, when the cl ock sele ct pi ns are c onfi gur e d so that ERCLK runs at 90 MHz; ROMCLK runs at 22.5 MHz.

The time that the Am79C976 controller waits for data to be valid is programmable. ROMTMG (CTRL0, bits 8-11 or BCR18, bits 15-12 ) defin es the time from w hen the Am79C976 controller drives ERA[19:0] with the Expansion ROM address to when the Am79C976 controller latches in the data on the ERD[7:0] inputs. The register value sp ec if i es th e t im e i n nu m be r of ROMCLK cycle s . When ROMTMG is set to nine (the default value), ERD[7:0] is sampled with the next rising edge of ROMCLK ten cycles after ERA[19:0 ] was dr iven with a new address value. The clock ed ge that is used to s ample

the data is also the clock edge tha t gen erate s the next Expansion ROM address. All four bytes of Expansion ROM data are stored in holding registers.

Because Expansion ROM accesses take longer than 16 PCI bus clock cycles, the PCI access will be disconnected with no d ata transfer after 15 cl ocks. Subsequent accesses will be retri ed until all four bytes have been read from the Expansion ROM.

The timing di agram in Figure 37 assumes th e default programming of ROMTMG (1001b = 9 CLK). After reading the first byte, the Am79C976 controller reads in three more bytes by incrementing the lower portion of the ROM address. The PCI bus logic generates disconnect/retry cycl es until all 32 bits are ready to be tran sferred over the PCI bus. When the host tries to perform a burst read of the Expansion ROM, th e Am79C976 controller will disconnect the access at the second data phase.

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The host must program the Expa ns ion ROM Bas e A ddress register (ROMBASE) in the PCI configuration space before the first access to the Expansion ROM. The Am79C976 contro ller will not react to any acce ss to the Expansion ROM until both MEMEN (PC I Command register, bit 1) and ROMEN (PCI Expansion ROM Base Address register, bit 0) are set to 1.

The amount of memor y s pac e tha t the A m79 C976 device will claim for the Ex pan si on ROM de pen ds on th e contents of the Expansion ROM Configuration Register (ROM_CFG), which should be loaded from the EEPROM. This register is i ncluded in the A m79C97 6 device so that the c ontr oller c an ac comm odate ROMs of different sizes without wa sting memory s pace. The

ROM occupies a block of memory space that is some power of two between 2K and 16 M i n si ze. If the ROM requires 2

bytes of address sp ace, bits 1 throu gh n- 1 of the Expansion ROM Base Address Register in P CI configuration space (ROMBA SE) should a ppear to be wired to 0. The contents of the Expansion ROM Configuration Register (ROM_CFG) determine how many bits of the configuration space register are forced to 0.

Bits [15:1] of ROM_CFG correspond to bits [23:9] of ROMBASE and bit 0 of ROM_CFG co rresponds to bit 0 of ROMBASE. If a bit in ROM_CFG is set to 0, the corresponding bit in ROMBASE is fixed at zero. If a bit in ROM_CFG is set to 1, the corresponding bit in ROM-

ROMCLK

ERA[19:0]

ERD[7:0]

FLCS

FLOE

FLWE

Page 94

94 Am79C976 8/01/00

PRELIMINARY

BASE can be programmed to 0 or 1 through PC I configuration space accesses to ROMBASE.

Bit 0 of ROM_CFG controls bit 0 of ROMBASE. If bit 0 of ROM_CFG is 0, the host CPU cannot write to bit 0 of ROMBASE. This bit is th e address decode en able bit. When this bit is fixed at 0, it will appear to the host CPU that the ROM Base Address Register and, therefore, the expansion ROM does not exist.

If bit 0 of ROM_CFG is set to 1, the host CPU is able to read and write bit 0 of ROMBASE.

As an example, if the Expa nsion ROM occupies 2

(65536) bytes, bits 15:9 of ROMBASE sho uld be f ixed at 0. Sinc e bits 15 :9 of R OMBASE ar e control led by bits 7:1 of ROM_CFG, bits 7:1 of ROM_CFG should be cleared to 0 and bits 15:8 shou ld be s et to 1. To make ROMBASE accessi ble to the host CPU, bit 0 of ROM_CFG should be set to 1. Therefore, ROM_CFG should be set to FF01h. If the host CPU writes all 1s to the ROMBASE register and then read s back the contents of ROMBASE, the result would be FFFF0001h.

After the host CPU has wr itte n to the E xpansi on ROM Base Address Register in PCI configuration space to map the ROM into PCI memory space and to enable accesses to the ROM, the address output to the Expansion ROM will be the offset from the address on the PCI bus to ROMBASE.

The Am79C976 controller aliases all accesses to the Expansion ROM of the command types Memory Read Multiple and Memory Read Line to the bas ic Memory Read command.

Since setting MEMEN also enables memory mapped access to the I/O resources, attention must be given to the PCI Memory Mapped I/O Base Address register, before enabling access to the Expansion ROM. The host must set the PCI Memor y Mapped I/O Bas e Address register to a value that prevents the Am79C976 controller from claiming any memory cycles not intended for it.

During the boot procedure, the system will try to find an Expansion ROM. A PCI system assumes that an Expansion ROM is present when it reads the ROM signature 55h (byte 0) and AAh (byte 1).

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In addition to mapping the Flash memor y in to PCI address space, the Am79 C976 c ontrolle r provide s an indirect read/write data path for programming the Flash memory. The Flash is ac cessed by first wr iting the

memory address to the Flash Address Register, and then reading or writing the Flash Data Register.

For software compatibility with older PCnet devices, the Flash device can also be accessed by a read or write to the Expansion Bus Data port (BCR30). The user must load the upper addr es s EPADDRU (BCR 29, bits 3-0). EPADDRU is not needed if the Flash size i s 64K or less, but still must be programmed. The user will then load the lower 16 bits of address, EP ADDRL (BCR 28, bits 15-0).

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A read to the Flash Data Register will start a read cycle on the External Memory Interface. The Am79C976 controller will drive ERD[11:8] with the 4 most significant address bits at the same time that it drives ERA[19:0] with the 20 least significant bits.

The FLCS

pin is driven low for the value ROMTMG + 1. Figure 38 assumes that ROMTMG is set to nine. ERD[7:0] is sampled with the next r ising edge of CLK ten clock cycles after ERA[19:0] was driven with a new address value. This PCI slave access to the Flash/ EPROM will result in a retry for the very first access. Subsequent accesses may give a retry or not, depending on whether or not the data is present and valid. The access time is dependen t on the ROMTMG bits (CTRL0, bits 11-8, or BCR18, bits 15-12) and c an be tuned for the particular memory device used.

This access mech anism using B CR28, 29 , an d 30 d iffers from the Expansion ROM access mechanism since only one byte is read in this ma nner, instead of the 4 bytes in an Expansion ROM access.

If the Lower Address Auto Increment (LAAINC) bit (FLASH_ADDR, bit 31 or BCR29, bit 14) is set, the EBADDRL address will be incremented and a continuous series of reads from the Expansion Data Port (FLASH_DATA or EBDATA, BCR30) is possible. The upper address field, EBADDRU, is not automatically incremented when t he lower address fie ld, EBADDRL rolls over.

The Flash write procedure is almost identical to the read access, except that the Am7 9C976 c ontr oller wi ll not drive FLOE

low. The FLCS and FLWE signals are driven low for the value ROMTMG again. The wri te to the FLASH port is a posted write and will not result in a retry to the PCI, unless the hos t tries to write a new value before the previous write is complete. Then the host will experience a retry . See Figure 3939.

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8/01/00 Am79C976 95

PRELIMINARY

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The Am79C976 controller uses external SSRAM for receive and transmit FIFOs. The size of the SSRA M ca n be up to 4 Mbytes, organized as 1M X 32 bits. The size of the SSRAM is indicated by the contents of the SSRAM Size Register (or BCR25). SRAM_SIZE should be loaded from the EEPROM.

The SSRAM is programmed in units of 512-byte pages. To spec ify how much of the SSRAM is allocated to transmit and how much is allocated to receive, the user should program SRAM_BND Regist er (or BC R26, bits 15-0) with the page boundary where the receive buffer begins. The SRAM_BND is also programmed in units of 512-byte pages. The transmit buffer space starts at 0000h. It is up to the user or the software driver to split up the memor y for transmit or receive; there is no defaulted value. The minimum SSRAM size required is

four 512-byte pages for each transmit and receive queue, which limits the SSRAM size to be at least 4 Kbytes.

The SRAM_BND upon H_RESET will be reset to 0000h. SRAM_B ND must be programm ed to a nonzero value if the transmitter is enabled. SRAM_BND should be programmed to a value larger than the maximum frame size to use the automatic retransmission options, REX_UFLO, REX_RTRY, and RTRY_LCOL, or if the transmit FIFO start point, XMTSP, is set to Full Frame. (XMTSP is CTRL1, bits 17-16, or CSR80, b its 11-10.)

The Am79C976 control ler does not allow software d iagnostic access to the SRAM as do older devices in the PCnet family. The Am79C976 controlle r provides software access to an internal memory built-in self-test (MBIST) controller which runs extensive, at-speed

ROMCLK

ERA[19:0]

FLCS

FLOE

ERD[7:0]

FLWE

ROMCLK

ERA[19:0]

FLCS

FLOE

ERD[7:0]

FLWE

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96 Am79C976 8/01/00

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tests on the external SRAM, internal SRAM access logic, and the PC board interconnect.

The MBIST controller can determine the size of the external SRAM and verify its operation using the following procedure:

1. Program SRAM_SIZE to the minimum allowed value of 4.

2. Write DM_START and DM_FAIL_STOP (write DATAMBIST bits 63:56 with 0x28). The remainder of the DATAMBIST register ignores writes so it may be written with arbitrary data or not written at all.

3. Read DM_DONE (DATAMBIST bit 63) and DM_ERROR (DATAMBIST bit 62) until D M_DONE is set.

4. If DM_ERROR is set, th e memory is defective; report the error and exit.

5. Program SRAM_SIZE to the maximum value of 0x8000 and repeat steps 2 and 3.

6. If DM_ERROR is zero, report the current value of SRAM_SIZE as the SSRAM size.

7. If DM_ERROR is set, program SRAM_SIZE to onehalf the maximum (0x4000) and repeat steps 2 and 3.

8. Repeat, using the binary search algorithm, until the SRAM size has been determine d.

EEPROM Interface

The Am79C976 device includes an int erface to an optional 16-bit word-or iented 93Cxx-compatible se rial EEPROM that supports automat ic ad dress i ncr ementing (seque ntial read ). This EEPROM can be used for storing initial values for Am79C976 registers. The contents of this EEPROM are automatically loaded into the selected registers after a reset operation or whenever the host CPU requests an EEROM read operation.

Note that if the EEPROM is not included in the system, the MAC address (and Magic Packet information, if needed) must be initialized by the host CPU.

The Am79C976 device automatically detects the size of the EEPROM. When the E EPROM decodes a read command, it drives its DO pin low when the A0 address bit is written to the DI pin. The Am79C976 device uses this fact to detect the number of bits in the EEPROM address and from this determines the EEPROM size.

Data in the EEPROM are inte rpreted as three-byte entries that contain register addr ess and register dat a so that the system designer can choose which registers will automatically be loaded. In a typical system, the EEPROM would be used to initialize the device’s IEEE 802 physical address, the PCI Subsystem V endor ID , LED configuration, SSRAM configuration, and other hardware configuration information. For compa tibility

with older PCnet family software the Address PROM Space should be loaded from the EEPROM. See the Address PROM Space section for details.

Only the memory-mapped registers can be loaded from the EEPROM. While the CSRs and BCRs are not memory-mapped, all useful bits in the CSRs and BCRs are aliased into memory-mapped registers so that all useful bits can be loaded from the EEPROM.

Most of the memory-mapped registers are 32 bits wide and occupy 4 bytes of memory space each. For example, the CMD2 Register is located at offset 50h from the memory base ad dress. Its least sig nificant 16 bits can be accessed at offse t 50h, and its mo st significant 1 6 bits can be access ed at offset 52h. Regis ter data are loaded from the EEPROM 16 bits at a time, so that the high order bits of a r egister are loaded in dependently from the low order bits.

The EEPROM Access Register gives the host CPU direct access to the interface pins so that it can read from or write to the EEPROM.

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After the trailing edge of the RES ET sign al or after th e PREAD bit in BCR19 is set, the Am79C976 device begins to read data from the EEPROM. Data from the EEPROM are interpreted as a string of 3-byte entries. Each entry contains a 1- byte register address and a 2-byte register data field. The register address field contains the offset of the target registe r divided by 2. The initialization logic writes the contents of the register data field into the register selecte d by the register address byte.

Since EEPROM data are loaded two bytes at a time, the least significant bit of the target register offset is omitted from the address field. Only bits 8:1 are included. Therefore, the register address byte contains the offset of the target registe r divided by two. For example, the Control2 Register (CTRL2) is a 32-bit register located at offset 70h ( rela tive to the co nten ts of th e Memory-M apped I/O Base Address Regi ster). Therefore, the byte stream 38h, 02h, 05h would cause the value 0205h to be loaded into bits [15:0] of CTRL2, and 39h, 00h, 03h would cause the value 0003h to be loaded into bits [31:16] of the same register.

If the value of the address byte is 0FFh, the following 2-byte field is inter preted a s a 16-bit CRC code rather than as register data. The CR C code covers all EEPROM data up to and including the address byte of the entry co ntaining the C RC. All EEPROM data after the CRC code word are ignored.

The CRC code used is CRC-16, which is based on the generator polynomial x

+ x15 + x2 + 1.

The EEPROM must contain data for an odd number of registers so that the CRC is aligned on a 16-bit word

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PRELIMINARY

boundary in the EEPROM. If an even number of registers need to be load ed from the EEPROM, two du plicate entries for the same register can be included so that the CRC is aligned properly.

For full compatibility with legacy Magic Packet software, the EEPROM should initialize both the APROM area (offset 0-0Fh) and the PADR Register.

Data are shifted into or out of th e EEPROM most significant bit first.

Figure 41 shows the mapping of the 3-byte entries into the 16-bit word-oriented EEPROM.

If the Am79C976 device detects a CRC error in the EEPROM or fails to detect the presence of an EEPROM, it restores all registers to their default values and clears the PVALID bit in BCR19 to indicate the error.

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98 Am79C976 8/01/00

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Note: All registers are restored to their default values, not just those regi sters that were altered by the E EPROM read operation.

If the Am79C976 device detects a correct CRC code, it sets the PVALID bit to 1 to indicate th at the regis ters have been successfully initialized.

The CPU can initiate an automatic EEPROM read operation at any time by setting the PREAD bit in BCR19 to 1.

The CPU cannot access any Am79C976 register while an automatic EEPROM read operation is in progress. If the CPU attempts to access a register during this time, the Am79C976 con troller w ill ter minat e the ac cess attempt by asser ting DEV SEL

and STOP while TRDY is not asserted, a co mbi nati on t hat in dicat es t hat the ini tiator must disconne ct and retr y the access at a la ter time. The automatic read operation takes about 180 µs for each 16-bit register that is initialized plus 180 µs for the CRC code word.

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When the address field of an EEPROM instruction is shifted in through the DI pin of the EEPROM, the EEPROM drives its DO pin low when the A0 bit appears on the DI pin. T he Am79C976 controller m akes

use of this feature to detect the presence of an EEPROM. When the device atte mpts to read the fi rst word from the EEPROM and if the EEDO pin is not driven lo w bef ore the 15th EESK clo ck cyc le, the d evice assumes that there is no EEPROM present.

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The user can directly ac cess the port through th e EEPROM Access Register (BCR19). This register contains bits that can be used to control the interface pins. By performing an appropriate sequence of accesses to BCR19, the user can effectively write to and read from the EEPROM. This feature may be used by a syste m configuration utility to program hardware c onfiguration information into the EEPROM.

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The EEPROM interface logic first shifts each 16-bit word from the EEPROM most significant bit first into an internal holding register. Then it shifts the word through the CRC logic least significant bit first, effectively swapping the bytes. Therefore, the data shown in Figure 42 are processed by the CRC logic in th e following order: DATA[15:8], ADR1, ADR2, DATA[7:0], DATA[7:0],

DATA[15:8], ... .

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LED Support

The Am79C976 controller can support up to four LEDs. LED outputs LED0

, LED1, and LED2 allow for direct

connection of an LED and its supporting pull-up device. In applications that want to use the pin to drive an LED

and also have an EEPROM, it might be necessary to buffer the LED3

circuit from the EEPROM conne ction .

When an LED circuit is directly co nnected to the

EEDO/LED3

/RXFRTGD pin, then it is not pos sible for

most EEPROM devices to sink enough I

to maintain a valid low level on the EEDO input to the Am7 9C976 controller. Use of buffering can be avoided if a low power LED is used.

Each LED can be programmed through a BCR register to indicate one or more of the following network statuses or activities: Collision Status, Full-Duplex Link

DATA[15:8]ADR1

ADR2DATA[7:0]

DATA[7:0]DATA[15:8]

DATA[15:8]ADR3

. . .

DATA[15:8]ADR1

CRC LOGIC

15 0

Holding Register

+ +

...

EEPROMAm79C976 Controller

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8/01/00 Am79C976 99

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Status, Receive Match, Receive Status, Magic Packet, Transmit Status, and Start Frame/Byte Delimiter.

The LED pins can be configur ed to operate in either open-drain mode (acti ve low) or in totem-pole mode (active high). The output can b e str etche d to a llow the human eye to recognize even short events that last only several microseconds. After H_RESET, the four LED outputs are configured as shown in Table 16.

For each LED register, each of the status signals is AND’d with its enable signal, and thes e signa ls are all OR’d together to form a combine d status signal. Eac h LED pin combined status signal can be programmed to run to a pulse stretcher, which consists of a 3-bit shi ft register clocked at 38 Hz (26 ms). The data in put of each shift register is norm ally at logic 0. The OR gat e output for each LED register asynchronously sets all three bits of its shift register when the output becomes asser ted. The invert ed output of eac h shift regis ter is used to control an L ED pin. Thus, the pulse s tretcher provides 2 to 3 cl ocks of stretche d LED output, or 52 ms to 78 ms. See Figure 4343.

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Power Savings Mode

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The Am79C976 controller supports power management as defined in the PCI Bus Power Management Interface Specification V1.1 and Network Device Class Power Management Reference Specification V1.0. These specifications define the networ k device power states, PCI power management interface includi ng th e Capabilities Data Structure and power management registers block definitions, power management events, and OnNow network Wake-up events. In addition, the Am79C976 controlle r su ppo rts legacy power m ana gement schemes, such as Remote Wake-Up (RWU) mode. The RWU mode can accommoda te systems that sleep with PCI bus power off or on and the PCI clock running or stopped. The RWU pin can dri ve the CPU's System Management Interrupt (SMI) line or a system power controller.

The general scheme for the Am79C976 controller power management is that when a wake-up event is detected, a signal is generate d to cause hard ware external to the Am79C976 device to put the computer into the working (S0) mode. The Am79C976 device supports three types of wake-up events:

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The Am79C976 device supports two types of wake-up control mechanisms:

Table 16. LED Default Configuration

LED

Output Indication Driver Mode Pulse Stretch

LED0 Link Status

Open Drain -

Active Low

Enabled

LED1 Activity

Open Drain -

Active Low

Enabled

LED2 Speed

Open Drain -

Active Low

Enabled

LED3 Coll

Open Drain -

Active Low

Enabled

COL

COLE

FDLS

FDLSE

LNKS

LNKSE

RCV

RCVE

RCVM

RCVME

XMT

XMTE

Pulse Stretcher

MR_SPEED_SEL

100E

MPS

MPSE

22929B-45

Page 100

100 Am79C976 8/01/00

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All three wake-up events and both control mechanisms support wake-up from any power state including D3

cold

(PCI bus power off and clock stopped ). Figure 44 shows the relationship between these Wake-up events and the various outputs u sed to signal t o the external hardware.

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The system software enables the PME pin by settin g the PME_EN bit in the PMCSR register (PCI configuration registers, offset 48 h, bit 8) to 1. W hen a Wake-up event is detected, the Am79C976 device sets the PME_STATUS bit in the PMCSR register (PCI configuration registers, offset 48h, bit 15). Setting this bit causes the PME

signal to be asserted.

Assertion of the PME

signal causes external hardware

to wake up the CPU. The system software then reads

the PMCSR register of every PCI device in the system to determine which device asserted the PME

signal.

When the software determines that the signal came from the Am79C976 device, it writes to the device’s PMCSR to put the device into power state D0. The software then writes a 0 to the PME_STATUS bit to clear the bit and turn off the P ME

signal, and it calls th e device’s software driver to tell it that the device is now in state D0. The system software can clear the PME_STATUS bit either before, after, or at the same time that it puts the device back into the D0 state.

MPDETECT

MPPEN_EE

MPEN_EE

MPINT LED

WUMI

Magic Packet

Link Change

LCMODE_EE

Link Change

MPMAT

LCDET

SET

CLR

PMAT1

SET

CLR

SET

CLR

SET

CLR

PMAT

Pattern Match

Input

Pattern

PME_STATUS

PME Status

PME_EN

MPMAT

PME_EN_OVR

LCEVENT

PME

RWU

SET

CLR

POR

H_RESET

POR

Data from PCI Bus

MPPEN_SW

MPEN_SW

PMAT0

Pattern Match RAM (PMR)

PMAT_MODE

LCMODE_SW