Datasheet DP83901AV Datasheet (NSC)

Page 1

DP83901A SNIC Serial Network Interface Controller

November 1995

General Description

The DP83901A Serial Network Interface Controller (SNIC) is a microCMOS VLSI device designed for easy implementation of CSMA/CD local area networks. These include Ethernet (10BASE5), Thin Ethernet (10BASE2) and Twisted-pair Ethernet (10BASE-T). The overall SNIC solution provides the Media Access Control (MAC) and Encode-Decode (ENDEC) functions in accordance with the IEEE 802.3 standard.

The integrated ENDEC module allows Manchester encoding and decoding via a differential transceiver and phase lock loop at 10 Mbit/sec. Also included is a collision detect translator and diagnostic loopback capability. (Continued)

1.0 System Diagram

Features

Compatible with IEEE 802.3, 10BASE5, 10BASE2, 10BASE-T

Dual 16-byte DMA channels

16-byte internal FIFO

Network statistics storage

Supports physical, multicast and broadcast address filtering

10 Mbit/sec Manchester encoding and decoding plus clock recovery

No external precision components required

Efficient buffer management implementation

Transmitter can be selected for half or full step mode

Integrated squelch on receive and collision pairs

3 levels of loopback supported

Utilizes independent system and network clocks

Lock Time 5 bits typical

Decodes Manchester data with up tog18 ns jitter

TL/F/10469– 1

TRI-STATEÉis a registered trademark of National Semiconductor Corporation.

1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

TL/F/10469

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General Description (Continued)

The MAC function (NIC) provides simple and efficient packet transmission and reception control by means of unique dual DMA channels and an internal FIFO. Bus arbitration and memory control logic are integrated to reduce board cost and area overheads.

SNIC used in conjunction with the DP8392 Coaxial Transceiver Interface (CTI) provides a comprehensive 2 chip solution for IEEE 802.3 networks and is designed for easy interface to the latest 10BASE-T transceivers.

Due to the inherent constraints of CMOS processing, isolation is required at the differential signal interfaces for 10BASE5 and 10BASE2 applications. Capacitive or inductive isolation may be used.

Connection Diagram

Table Of Contents

1.0 SYSTEM DIAGRAM

2.0 PIN DESCRIPTION

3.0 BLOCK DIAGRAM

4.0 FUNCTIONAL DESCRIPTION

5.0 TRANSMIT/RECEIVE PACKET ENCAPSULATION/DECAPSULATION

6.0 DIRECT MEMORY ACCESS CONTROL (DMA)

7.0 PACKET RECEPTION

8.0 PACKET TRANSMISSION

9.0 REMOTE DMA

10.0 INTERNAL REGISTERS

11.0 INITIALIZATION PROCEDURE

12.0 LOOPBACK DIAGNOSTICS

13.0 BUS ARBITRATION

14.0 PRELIMINARY ELECTRICAL CHARACTERISTICS

15.0 SWITCHING CHARACTERISTICS

16.0 AC TIMING TEST CONDITIONS

17.0 PHYSICAL DIMENSIONS

Top View

Order Number DP83901AV

See NS Package Number V68A

TL/F/10469– 2

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Pin Description

Pin No Pin Name I/O Description

BUS INTERFACE PINS

2 PRD O PORT READ: Enables data from external latch on to local bus during a memory write cycle to

3–6 RA0–RA3 I REGISTER ADDRESS: These four pins are used to select a register to be read or written. The

7–17, AD0– AD15 I/O, Z MULTIPLEXED ADDRESS/DATA BUS:

19,

22–25 used to read and write register data. AD8–AD15 float during I/O transfers, SRD, SWR pins are

26 ADS0 I/O, Z ADDRESS STROBE 0:

27 CS O CHIP SELECT: Chip Select places controller in slave mode for mP access to internal registers.

28 MWR O, Z MASTER WRITE STROBE: (Strobe for DMA transfers)

29 MRD O, Z MASTER READ STROBE: (Strobe for DMA transfers)

30 SWR I SLAVE WRITE STROBE: Strobe from CPU to write an internal register selected by RA0 –RA3.

31 SRD I SLAVE READ STROBE: Strobe from CPU to read an internal register selected by RA0 –RA3.

32 ACK O ACKNOWLEDGE: Active low when SNIC grants access to CPU. Used to insert WAIT states to

34 BSCK I BUS CLOCK: This clock is used to establish the period of the DMA memory cycle. Four clock

36 RACK I READ ACKNOWLEDGE: Indicates that the system DMA or host CPU has read the data placed

37 PWR O PORT WRITE: Strobe used to latch data from the SNIC into external latch for transfer to host

38 READY I READY: This pin is set high to insert wait states during a DMA transfer. The SNIC will sample this

local memory (remote write operation). This allows asynchronous transfer of data from the system memory to local memory.

state of these inputs is ignored when the NIC is not in slave mode (CS

used to select direction of transfer. Bus Master with BACK input asserted.

During t1 of memory cycle AD0–AD15 contain address. During t2, t3, t4 AD0–AD15 contain data (word transfer mode). During t2, t3, t4 AD0–AD7 contain data, AD8 –AD15 contain address (byte transfer mode). Direction of transfer is indicated by SNIC on MWR

Input: with DMA inactive and CS low, latches RA0–RA3 inputs on falling edge. If high, data

present on RA0–RA3 will flow through latch. Output: When Bus Master, latches address bits (A0–A15) to external memory during DMA

transfers.

Must be valid through data portion of bus cycle. RA0–RA3 are used to select the internal register. SWR and SRD select direction of data transfer.

Active low during write cycles (t2, t3, tw) to buffer memory. Rising edge coincides with the presence of valid output data. TRI-STATE

Active during read cycles (t2, t3, tw) to buffer memory. Input data must be valid on rising edge of MRD. TRI-STATE until BACK asserted.

Data is latched into the SNIC on the rising edge of this input.

The register data is output when SRD

CPU until SNIC is synchronized for a register read or write operation.

cycles (t1, t2, t3, t4) are used per DMA cycle. DMA transfers can be extended by one BSCK increments using the READY input.

in the external latch by the SNIC. The SNIC will begin a read cycle to update the latch.

memory during Remote Read transfers. The rising edge of PWR valid data on the local bus.

signal at t3 during DMA transfers.

goes low.

, MRD lines.

until BACK asserted.

high).

coincides with the presence of

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Pin Description (Continued)

Pin No Pin Name I/O Description

BUS INTERFACE PINS (Continued)

39 PRQ/ADS1 O, Z PORT REQUEST/ADDRESS STROBE 1

40 BACK I BUS ACKNOWLEDGE: Bus Acknowledge is an active high signal indicating that the CPU has

41 BREQ O BUS REQUEST: Bus Request is an active high signal used to request the bus for DMA transfers.

65 RESET I RESET: Reset is active low and places the SNIC in a reset immediately, no packets are

67 INT O INTERRUPT: Indicates that the SNIC requires CPU attention after reception transmission or

68 WACK I WRITE ACKNOWLEDGE: Issued from system to SNIC to indicate that data has been written to

NETWORK INTERFACE PINS

42, TX

43 TX

b a

46 TEST I FACTORY TEST INPUT: Used to check the chip’s internal functions. Tied low during normal

47 SEL I MODE SELECT: When high, Transmitaand Transmitbare the same voltage in the idle state.

50 X1 I EXTERNAL OSCILLATOR INPUT

51 GND/X2 O GROUND/X2: This in should normally be connected to ground. It is possible to use a crystal

56 SNISEL I FACTORY TEST INPUT: For normal operation tied to VCC. When low enables the ENDEC

60, RX

61 RX

62, CD

63 CD

b a

32-BIT MODE: If LAS is set in the Data Configuration Register, this line is programmed

as ADS1

. It is used to strobe addresses A16–A31 into external latches. (A16 –A31 are the

fixed addresses stored in RSAR0, RSAR1). ADS1

will remain at TRI-STATE until BACK is

received. 16-BIT MODE: If LAS is not set in the Data Configuration Register, this line is programmed as

PRQ and is used for Remote DMA Transfers. The SNIC initiates a single remote DMA read or write operation by asserting this pin. In this mode PRQ will be a standard logic output.

Note: This line will power up as TRI-STATE until the Data Configuration Register is programmed.

granted the bus to the SNIC. If immediate bus access is desired, BREQ should be tied to BACK.

Tying BACK to V

will result in a deadlock.

This signal is automatically generated when the FIFO needs servicing.

transmitted or received by the SNIC until STA bit is set. Affects Command Register, Interrupt Mask Register, Data Configuration Register and Transmit Configuration Register. The SNIC will execute reset within 10 BSCK cycles and TXC cycles.

completion of DMA transfers. The interrupt is cleared by writing to the ISR (Interrupt Service Register). All interrupts are maskable.

the external latch. The SNIC will begin a write cycle to place the data in local memory.

O TRANSMIT OUTPUT: Differential driver which sends the encoded data to the transceiver. The

outputs are source followers which require 270X pulldown resistors.

operation.

When low, Transmit

is positive with respect to Transmitbin the idle state, at the transformer’s

primary.

oscillator using X1 and GND/X2 if certain precautions are taken. Contact National Semiconductor for more information.

module to be tested independently of the SNIC module.

I RECEIVE INPUT: Differential receive input pair from the transceiver.

I COLLISION INPUT: Differential collision pair input from the transceiver.

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Pin Description (Continued)

Pin No Pin Name I/O Description

POWER SUPPLY PINS

21, 48, V

53, 55

20, 33, 49 GND DIGITAL NEGATIVE (GROUND) SUPPLY PINS: It is suggested that a decoupling capacitor be

54, 66

59 V

64 GND AUI RECEIVE GROUND: Ground pin for AUI receiver.

45 V

44 GND AUI TRANSMIT GROUND: Ground pin for AUI transmitter

58 V

57 GND VCO GROUND PIN: Care should be taken to reduce noise on this pin as it is the ground to the

NO CONNECTION

1, 18, NC NO CONNECTION: Do not connect to these pins.

35, 52

DIGITAL POSITIVE 5V SUPPLY PINS:

connected between the V

AUI RECEIVE 5V SUPPLY: Power pin supplies 5V to the AUI receiver.

AUI TRANSMIT 5V SUPPLY: Power pin supplies 5V to the AUI transmitter.

VCO 5V SUPPLY: Care should be taken to reduce noise on this pin as it supplies 5V to the

ENDEC’s Phase Lock Loop.

and GND pins.

3.0 Block Diagram

FIGURE 1

TL/F/10469– 3

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4.0 Functional Description (Refer to

Figure 1

ENCODER/DECODER (ENDEC) MODULE

The ENDEC consists of four main logical blocks:

a) The Manchester encoder accepts NRZ data from the

controller, encodes the data to Manchester, and transmits it differentially to the transceiver, through the differential transmit driver.

b) The Manchester decoder receives Manchester data from

the transceiver, converts it to NRZ data and clock pulses, and sends it to the controller.

c) The collision translator indicates to the controller the

presence of a valid 10 MHz collision signal to the PLL.

MANCHESTER ENCODER AND DIFFERENTIAL DRIVER

The differential transmit pair, on the secondary of the employed transformer, drives up to 50 meters of twisted pair AUI cable. These outputs are source followers which require two 270X pull-down resistors to ground.

The DP83901A allows both half-step and full-step to be compatible with Ethernet and IEEE 802.3. With the SEL pin low (for Ethernet I). Transmit

Transmit Transmit provides zero differential voltage to operate with transformer coupled loads.

MANCHESTER DECODER

The decoder consists of a differential receiver and a PLL to separate a Manchester decoded data stream into internal clock signals and data. The differential input must be externally terminated with two 39X resistors connected in series if the standard 78X transceiver drop cable is used, in thin Ethernet applications, these resistors are optional. To prevent noise from falsely triggering the decoder, a squelch circuit at the input rejects signals with levels less than

175 mV. Signals more negative thanb300 mV and a duration greater than 30 ns are decoded. Data becomes valid typically within 5 bit times. The DP83901A may tolerate bit jitter up to 18 ns in the received data. The decoder detects the end of a frame when no more mid-bit transitions are detected.

COLLISION TRANSLATOR

When the Ethernet transceiver (DP8392 CTI) detects a collision, it generates a 10 MHz signal to the differential collision inputs (CD tected active, the DP83901A uses this signal to back off its current transmission and reschedule another one.

The collision differential inputs are terminated the same way as the differential receive inputs. The squelch circuitry is also similar, rejecting pulses with levels less than

during idle; with SEL high (for IEEE 802.3),

and Transmitbare equal in the idle state. This

) of the DP83901A. When these inputs are de-

is positive with respect to

175 mV.

)

NIC (Media Access Control) MODULE

RECEIVE DESERIALIZER

The Receive Deserializer is activated when the input signal Carrier Sense is asserted to allow incoming bits to be shifted into the shift register by the receive clock. The serial receive data is also routed to the CRC generator/checker. The Receive Deserializer includes a synch detector which detects the SFD (Start of Frame Delimiter) to establish where byte boundaries within the serial bit stream are located. After every eight receive clocks, the byte wide data is transferred to the 16-byte FIFO and the Receive Byte Count is incremented. The first six bytes after the SFD are checked for valid comparison by the Address Recognition Logic. If the Address Recognition Logic does not recognize the packet, the FIFO is cleared.

CRC GENERATOR/CHECKER

During transmission, the CRC logic generates a local CRC field for the transmitted bit sequence. The CRC encodes all fields after the SFD. The CRC is shifted out MSB first following the last transmit byte. During reception the CRC logic generates a CRC field from the incoming packet. This local CRC is serially compared to the incoming CRC appended to the end of the packet by the transmitting node. If the local and received CRC match, a specific pattern will be generated and decoded to indicate no data errors. Transmission errors result in different pattern and are detected, resulting in rejection of a packet (if so programmed).

TRANSMIT SERIALIZER

The Transmit Serializer reads parallel data from the FIFO and serializes it for transmission. The serializer is clocked by the transmit clock generated internally. The serial data is also shifted into the CRC generator/checker. At the beginning of each transmission, the Preamble and Synch Generator append 62 bits of 1,0 preamble and a 1,1 synch pattern. After the last data byte of the packet has been serialized the 32-bit FCS field is shifted directly out of the CRC generator. In the event of a collision the Preamble and Synch generator is used to generate a 32-bit JAM pattern of all 1’s.

ADDRESS RECOGNITION LOGIC

The address recognition logic compares the Destination Address Field (first 6 bytes of the received packet) to the Physical address registers stored in the Address Register Array. If any one of the six bytes does not match the pre-programmed physical address, the Protocol Control Logic rejects the packet. All multicast destination addresses are filtered using a hashing technique. (See register description.) If the multicast address indexes a bit that has been set in the filter bit array of the Multicast Address Register Array the packet is accepted, otherwise it is rejected by the Proto-

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4.0 Functional Description (Continued)

col Control Logic. Each destination address is also checked for all 1’s which is the reserved broadcast address.

FIFO AND BUS OPERATIONS

Overview

To accommodate the different rates at which data comes from (or goes to) the network and goes to (or comes from) the system memory, the SNIC contains a 16-byte FIFO for buffering data between the media. The FIFO threshold is programmable, allowing filling (or emptying) the FIFO at different rates. When the FIFO has filled to its programmed threshold, the local DMA channel transfers these bytes (or words) into local memory. It is crucial that the local DMA is given access to the bus within a minimum bus latency time; otherwise a FIFO underrun (or overrun) occurs.

FIFO underruns or overruns are caused by two conditions: (1) the bus latency is so long that the FIFO has filled (or emptied) from the network before the local DMA has serviced the FIFO and (2) the bus latency has slowed the throughput of the local DMA to point where it is slower than the network data rate (10 Mbit/sec). This second condition is also dependent upon DMA clock and word width (byte wide or word wide). The worst case condition ultimately limits the overall bus latency which the SNIC can tolerate.

Beginning of Receive

At the beginning or reception, the SNIC stores entire Address field of each incoming packet in the FIFO to determine whether the packet matches its Physical Address Registers or maps to one of its Multicast Registers. This causes the FIFO to accumulate 8 bytes. Furthermore, there are some synchronization delays in the DMA PLA. Thus, the actual time that BREQ is asserted from the time the Start of Frame Delimiter (SFD) is detected is 7.8 ms. This operation affects the bus latencies at 2 and 4-byte thresholds during the first receive BREQ since the FIFO must be filled to 8 bytes (or 4 words) before issuing a BREQ.

End of Receive

When the end of a packet is detected by the ENDEC module, the SNIC enters its end of packet processing sequence, emptying its FIFO and writing the status information at the beginning of the packet. The SNIC holds onto the bus for the entire sequence. The longest time BREQ may be extended occurs when a packet ends just as the SNIC performs its last FIFO burst. The SNIC, in this case, performs a programmed burst transfer followed by flushing the remaining bytes in the FIFO, and completed by writing the header information to memory. The following steps occur during this sequence.

1. SNIC issues BREQ because the FIFO threshold has been reached.

2. During the burst, packet ends, resulting in BREQ extended.

3. SNIC flushes remaining bytes from FIFO.

4. SNIC performs internal processing to prepare for writing the header.

5. SNIC writes 4-byte (2-word) header.

6. SNIC de-asserts BREQ.

FIFO Threshold Detection

To assure that no overwriting of data in the FIFO, the FIFO logic flags a FIFO overrun as the 13th byte is written into the FIFO, effectively shortening the FIFO to 13 bytes. The FIFO logic also operates differently in Byte Mode and in Word Mode. In Byte Mode, a threshold is indicated when the n byte has entered the FIFO; thus, with an 8-byte threshold, the SNIC issues Bus Request (BREQ) when the 9th byte has entered the FIFO. For Word Mode, BREQ is not generated until the n a 4 word threshold (equivalent to 8-byte threshold), BREQ is issued when the 10th byte has entered the FIFO.

Beginning of Transmit

Before transmitting, the SNIC performs a prefetch from memory to load the FIFO. The number of bytes prefetched is the programmed FIFO threshold. The next BREQ is not issued until after the SNIC actually begins transmitting data, i.e., after SFD.

Reading the FIFO

During normal operation, the FIFO must not be read. The SNIC will not issue an ACKnowledge back to the CPU if the FIFO is read. The FIFO should only be read during loopback diagnostics.

PROTOCOL PLA

The protocol PLA is responsible for implementing the IEEE

802.3 protocol, including collision recovery with random

backoff. The Protocol PLA also formats packets during transmission and strips preamble and synch during reception.

DMA AND BUFFER CONTROL LOGIC

The DMA and Buffer Control Logic is used to control two 16-bit DMA channels. During reception, the local DMA stores packets in a receive buffer ring, located in buffer memory. During transmission the Local DMA uses programmed pointer and length registers to transfer a packet from local buffer memory to the FIFO. A second DMA channel is used as a slave DMA to transfer data between the local buffer memory and the host system. The Local DMA and Remote DMA are internally arbitrated, with the Local DMA channel having highest priority. Both DMA channels use a common external bus clock to generate all required bus timing. External arbitration is performed with a standard bus request, bus acknowledge handshake protocol.

2 bytes have entered the FIFO. Thus, with

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5.0 Transmit/Receive Packet Encapsulation/Decapsulation

A standard IEEE 802.3 packet consists of the following fields: preamble, Start of Frame Delimiter (SFD), destination address, source address, length, data, and Frame Check Sequence (FCS). The typical format is shown in

Figure 2.

The packets are Manchester encoded and decoded by the ENDEC module and transferred serially to the NIC module using NRZ data with a clock. All fields are of fixed length except for the data field. The SNIC generates and appends the preamble, SFD and FCS field during transmission. The Preamble and SFD fields are stripped during reception. (The CRC is passed through to buffer memory during reception.)

PREAMBLE AND START OF FRAME DELIMITER (SFD)

The Manchester encoded alternating 1,0 preamble field is used by the ENDEC to acquire bit synchronization with an incoming packet. When transmitted each packet contains 62 bits of alternating 1,0 preamble. Some of this preamble will be lost as the packet travels through the network. The preamble field is stripped by the NIC module. Byte alignment is performed with the Start of Frame Delimiter (SFD) pattern which consists of two consecutive 1’s. The SNIC does not treat the SFD pattern as a byte, it detects only the two bit pattern. This allows any preceding preamble within the SFD to be used for phase locking.

DESTINATION ADDRESS

The destination address indicates the destination of the packet on the network and is used to filter unwanted packets from reaching a node. There are three types of address formats supported by the SNIC: physical, multicast and broadcast. The physical address is a unique address that corresponds only to a single node. All physical addresses have an MSB of ‘‘0’’. These addresses are compared to the internally stored physical address registers. Each bit in the destination address must match in order for the SNIC to accept the packet. Multicast addresses begin with an MSB

of ‘‘1’’. The SNIC filters multicast addresses using a standard hashing algorithm that maps all multicast addresses into a 6-bit value. This 6-bit value indexes a 64-bit array that filters the value. If the address consists of all 1’s it is a broadcast address, indicating that the packet is intended for all nodes. A promiscuous mode allows reception of all packets: the destination address is not required to match any filters. Physical, broadcast, multicast, and promiscuous address modes can be selected.

SOURCE ADDRESS

The source address is the physical address of the node that sent the packet. Source addresses cannot be multicast or broadcast addresses. This field is simply passed to buffer memory.

LENGTH FIELD

The 2-byte length field indicates the number of bytes that are contained in the data field of the packet. This field is not interpreted by the SNIC.

DATA FIELD

The data field consists of anywhere from 46 to 1500 bytes. Messages longer than 1500 bytes need to be broken into multiple packets. Messages shorter than 46 bytes will require appending a pad to bring the data field to the minimum length of 46 bytes. If the data field is padded, the number of valid data bytes is indicated in the length field. The SNIC

does not strip or append pad bytes for short packets, or check for oversize packets.

FCS FIELD

The Frame Check Sequence (FCS) is a 32-bit CRC field calculated and appended to a packet during transmission to allow detection of errors when a packet is received. During reception, error free packets result in a specific pattern in the CRC generator. Packets with improper CRC will be rejected. The AUTODIN II (X

polynomial is used for the CRC calculations.

FIGURE 2

TL/F/10469– 5

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6.0 Direct Memory Access Control (DMA)

The DMA capabilities of the SNIC greatly simplify the use of the DP83901A in typical configurations. The local DMA channel transfers data between the FIFO and memory. On transmission, the packet is DMA’d from memory to the FIFO in bursts. Should a collision occur (up to 15 times), the packet is retransmitted with no processor intervention. On reception, packets are DMAed from the FIFO to the receive buffer ring (as explained below).

A remote DMA channel is also provided on the SNIC to accomplish transfers between a buffer memory and system memory. The two DMA channels can alternatively be combined to form a single 32-bit address with 8- or 16-bit data.

DUAL DMA CONFIGURATION

An example configuration using both the local and remote DMA channels is shown below. Network activity is isolated

Dual Bus System

on a local bus, where the SNIC’s local DMA channel performs burst transfers between the buffer memory and the SNIC’s FIFO. The Remote DMA transfers data between the buffer memory and the host memory via a bidirectional I/O port. The Remote DMA provides local addressing capability and is used as a slave DMA by the host. Host side addressing must be provided by a host DMA or the CPU. The SNIC allows Local and Remote DMA operations to be interleaved.

SINGLE CHANNEL DMA OPERATION

If desirable, the two DMA channels can be combined to provide a 32-bit DMA address. The upper 16 bits of the 32-bit address are static and are used to point to a 64 kbyte (or 32k word) page of memory where packets are to be received and transmitted.

TL/F/10469– 6

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7.0 Packet Reception

The Local DMA receive channel uses a Buffer Ring Structure comprised of a series of contiguous fixed length 256-byte (128 word) buffers for storage of received packets. The location of the Receive Buffer Ring is programmed in two registers, a Page Start and a Page Stop Register. Ethernet packets consist of a distribution of shorter link control packets and longer data packets, the 256-byte buffer length provides a good compromise between short packets and longer packets to most efficiently use memory. In addition these buffers provide memory resources for storage of back-to-back packets in loaded networks. The assignment of buffers for storing packets is controlled by Buffer Management Logic in the SNIC. The Buffer Management Logic

NIC Receive Buffer Ring

provides three basic functions: linking receive buffers for long packets, recovery of buffers when a packet is rejected, and recirculation of buffer pages that have been read by the host.

At initialization, a portion of the 64 kbyte (or 32k word) address space is reserved for the receive buffer ring. Two 8-bit registers, The Page Start Address Register (PSTART) and the Page Stop Address Register (PSTOP) define the physical boundaries of where the buffers reside. The SNIC treats the list of buffers as a logical ring; whenever the DMA address reaches the Page Stop Address, the DMA is reset to the Page Start Address.

TL/F/10469– 7

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7.0 Packet Reception (Continued)

INITIALIZATION OF THE BUFFER RING

Two static registers and two working registers control the operation of the Buffer Ring. These are the Page Start Register, Page Stop Register (both described previously), the Current Page Register and the Boundary Pointer Register. The Current Page Register points to the first buffer used to store a packet and is used to restore the DMA for writing status to the Buffer Ring or for restoring the DMA address in the event of a Runt packet, a CRC, or Frame Alignment error. The Boundary Register points to the first packet in the Ring not yet read by the host. If the local DMA address ever reaches the Boundary, reception is aborted. The Boundary Pointer is also used to initialize the Remote DMA for removing a packet and is advanced when a packet is removed. A

Buffer Ring at Initialization

simple analogy to remember the function of these registers is that the Current Page Register acts as a Write Pointer and the Boundary Pointer acts as a Read Pointer.

Note: At initialization, the Page Start Register value should be loaded into

both the Current Page Register and the Boundary Pointer Register.

Note: The Page Start Register must not be initialized to 00H.

BEGINNING OF RECEPTION

When the first packet begins arriving the SNIC begins storing the packet at the location pointed to by the Current Page Register. An offset of 4 bytes is saved in this first buffer to allow room for storing receive status corresponding to this packet.

Received Packet Enters the Buffer Pages

TL/F/10469– 8

TL/F/10469– 9

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7.0 Packet Reception (Continued)

LINKING RECEIVE BUFFER PAGES

If the length of the packet exhausts the first 256-byte buffer, the DMA performs a forward link to the next buffer to store the remainder of the packet. For a maximal length packet the buffer logic will link six buffers to store the entire packet. Buffers cannot be skipped when linking, a packet will always be stored in contiguous buffers. Before the next buffer can be linked, the Buffer Management Logic performs two comparisons. The first comparison tests for equality between the DMA address of the next buffer and the contents of the Page Stop Register. If the buffer address equals the Page Stop Register, the buffer management logic will restore the DMA to the first buffer in the Receive Buffer Ring value programmed in the Page Start Address Register. The second comparison tests for equality between the DMA ad-

Linking Receive Buffer Pages

dress of the next buffer address and the contents of the Boundary Pointer Register. If the two values are equal the reception is aborted. The Boundary Pointer Register can be used to protect against overwriting any area in the receive buffer ring that has not yet been read. When linking buffers, buffer management will never cross this pointer, effectively avoiding any overwrites. If the buffer address does not match either the Boundary Pointer or Page Stop Address, the link to the next buffer is performed.

Linking Buffers

Before the DMA can enter the next contiguous 256-byte buffer, the address is checked for equality to PSTOP and to the Boundary Pointer. If neither are reached, the DMA is allowed to use the next buffer.

1) Check foreto PSTOP

2) Check for

to Boundary

TL/F/10469– 10

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7.0 Packet Reception (Continued)

Buffer Ring Overflow

If the Buffer Ring has been filled and the DMA reaches the Boundary Pointer Address, reception of the incoming packet will be aborted by the SNIC. Thus, the packets previously received and still contained in the Ring will not be destroyed.

In heavily loaded network which cause overflows of the Receive Buffer Ring, the SNIC may disable the local DMA and suspend further receptions even if the Boundary register is advanced beyond the Current register. To guarantee this will not happen, a software reset must be issued during all Receive Buffer Ring overflows (indicated by the OVW bit in the Interrupt Status Register). The following procedure is required to recover from a Receiver Buffer Ring Overflow.

If this routine is not adhered to, the SNIC may act in an unpredictable manner. It should also be noted that it is not permissible to service an overflow interrupt by continuing to empty packets from the receive buffer without implementing the prescribed overflow routine. A flow chart of the SNIC’s overflow routine can be found on the next page.

Note: It is necessary to define a variable in the driver, which will be called

‘‘Resend’’.

1. Read and store the value of the TXP bit in the SNIC’s Command Register.

2. Issue the STOP command to the SNIC. This is accomplished by setting the STP bit in the SNIC’s Command Register. Writing 21H to the Command Register will stop the SNIC.

3. Wait for at least 1.6 ms. Since the SNIC will complete any transmission or reception that is in progress, it is necessary to time out for the maximum possible duration of an Ethernet transmission or reception. By waiting

1.6 ms this is achieved with some guard band added. Previously, it was recommended that the RST bit of the Interrupt Status Register be polled to insure that the pending transmission or reception is completed. This bit is not a reliable indicator and subsequently should be ignored.

4. Clear the SNIC’s Remote Byte Count registers (RBCR0 and RBCR1).

5. Read the stored value of the TXP bit from step 1, above.

If this value is a 0, set the ‘‘Resend’’ variable toa0and jump to step 6.

If this value is a 1, read the SNIC’s Interrupt Status Register. If either the Packet Transmitted bit (PTX) or Trans-

Received Packet Aborted If It Hits Boundary

mit Error bit (TXE) is set to a 1, set the ‘‘Resend’’ variable to a 0 and jump to step 6. If neither of these bits is set, placea1inthe‘‘Resend’’ variable and jump to step

This step determines if there was a transmission in progress when the stop command was issued in step 2. If there was a transmission in progress, the SNIC’s ISR is read to determine whether or not the packet was recognized by the SNIC. If neither the PTX nor TXE bit was set, then the packet will essentially be lost and re-transmitted only after a time-out takes place in the upper level software. By determining that the packet was lost at the driver level, a transmit command can be reissued to the SNIC once the overflow routine is completed (as in step 11). Also, it is possible for the SNIC to defer indefinitely, when it is stopped on a busy network. Step 5 also alleviates this problem. Step 5 is essential and should not be omitted from the overflow routine, in order for the SNIC to operate correctly.

6. Place the SNIC in either mode 1 or mode 2 loopback. This can be accomplished by setting bits D2 and D1, of the Transmit Configuration Register, to ‘‘0,1’’ or ‘‘1,0’’, respectively.

7. Issue the START command to the SNIC. This can be accomplished by writing 22H to the Command Register. This is necessary to activate the SNIC’s Remote DMA channel.

8. Remove one or more packets from the receive buffer ring.

9. Reset the overwrite warning (OVW, overflow) bit in the Interrupt Status Register.

10. Take the SNIC out of loopback. This is done by writing the Transmit Configuration Register with the value it contains during normal operation. (Bits D2 and D1 should both be programmed to 0.)

11. If the ‘‘Resend’’ variable is set to a 1, reset the ‘‘Resend’’ variable and reissue the transmit command. This is done by writing a value of 26H to the Command Register. If the ‘‘Resend’’ variable is 0, nothing needs to be done.

Note 1: If Remote DMA is not being used, the SNIC does not need to be started before packets can be removed from the receive buffer ring. Hence, step 8 could be done before step 7.

Note 2: When the SNIC is in STOP mode, the Missed Talley Counter is disabled.

TL/F/10469– 11

Page 14

7.0 Packet Reception (Continued)

Overflow Routine Flow Chart

TL/F/10469– 52

Page 15

7.0 Packet Reception (Continued)

Enabling the SNIC On An Active Network

After the SNIC has been initialized the procedure for disabling and then re-enabling the SNIC on the network is similar to handling Receive Buffer Ring overflow as described previously.

1. Program Command Register for page 0 (Command

2. Initialize Data Configuration Register (DCR)

3. Clear Remote Byte Count Registers (RBCR0, RBCR1)

4. Initialize Receive Configuration Register (RCR)

5. Place the SNIC in LOOPBACK mode 1 or 2 (Transmit

6. Initialize Receive Buffer Ring: Boundary Pointer

7. Clear Interrupt Status Register (ISR) by writing 0FFH to

8. Initialize Interrupt Mask Register (IMR)

9. Program Command Register for page 1 (Command

Configuration Register

(BNDRY), Page Start (PSTART), and Page Stop (PSTOP)

it.

i) Initialize Physical Address Registers (PAR0 –PAR5)

ii) Initialize Multicast Address Registers (MAR0 –MAR7)

iii) Initialize CURRent pointer

21H)

02H or 04H)

61H)

Termination of Received PacketÐPacket Accepted

10) Put SNIC in START mode (Command Register The local receive DMA is still not active since the SNIC is in LOOPBACK.

11) Initialize the Transmit Configuration for the intended value. The SNIC is now ready for transmission and reception.

END OF PACKET OPERATIONS

At the end of the packet the SNIC determines whether the received packet is to be accepted or rejected. It either branches to a routine to store the Buffer Header or to another routine that recovers the buffers used to store the packet.

SUCCESSFUL RECEPTION

If the packet is successfully received, the DMA is restored to the first buffer used to store the packet (pointed to by the Current Page Register). The DMA then stores the Receive Status, a Pointer to where the next packet will be stored (Buffer 4) and the number of received bytes. Note that the remaining bytes in the last buffer are discarded and reception of the next packet begins on the next empty 256-byte buffer boundary. The Current Page Register is then initialized to the next available buffer in the Buffer Ring. (The location of the next buffer had been previously calculated and temporarily stored in an internal scratchpad register.)

22H).

TL/F/10469– 12

Page 16

7.0 Packet Reception (Continued)

BUFFER RECOVERY FOR REJECTED PACKETS

If the packet is a runt packet or contains CRC or Frame Alignment errors, it is rejected. The buffer management logic resets the DMA back to the first buffer page used to store the packet (pointed to by CURR), recovering all buffers that had been used to store the rejected packet. This operation will not be performed if the SNIC is programmed to accept either runt packets or packets with CRC or Frame Alignment

Termination of Receive PacketÐPacket Reject

errors. The received CRC is always stored in buffer memory after the last byte of received data for the packet.

Error Recovery

If the packet is rejected as shown, the DMA is restored by the SNIC by reprogramming the DMA starting address pointed to by the Current Page Register.

TL/F/10469– 13

Page 17

7.0 Packet Reception (Continued)

REMOVING PACKETS FROM THE RING

Packets are removed from the ring using the Remote DMA or an external device. When using the Remote DMA the Send Packet command can be used. This programs the Remote DMA to automatically remove the received packet pointed to by the Boundary Pointer. At the end of the transfer, the SNIC moves the Boundary Pointer, freeing additional buffers for reception. The Boundary Pointer can also be moved manually by programming the Boundary Register.

STORAGE FORMAT FOR RECEIVED PACKETS

The following diagrams describe the format for how received packets are placed into memory by the local DMA channel. These modes are selected in the Data Configuration Register.

AD15 AD8 AD7 AD0

Next Packet Pointer Receive Status

Receive Byte Count 1 Receive Byte Count 0

Byte 2 Byte 1

BOSe0, WTSe1 in Data Configuration Register. This format is used with Series 32xxx, or 808xx processors.

1st Received Packet Removed by Remote DMA

AD15 AD8 AD7 AD0

Next Packet Pointer Receive Status

Receive Byte Count 0 Receive Byte Count 1

Byte 1 Byte 2

BOSe1, WTSe1 in Data Configuration Register. This format is used with 680x0 type processors. (Note: The Receive Count ordering remains the same for BOS

0or1.)

Receive Status

Next Packet Pointer

Receive Byte Count 0

Receive Byte Count 1

Byte 0

Byte 1

BOSe0, WTSe0 in Data Configuration Register. This format is used with general 8-bit processors.

TL/F/10469– 14

Page 18

8.0 Packet Transmission

The Local DMA is also used during transmission of a packet. Three registers control the DMA transfer during transmission, a Transmit Page Start Address Register (TPSR) and the Transmit Byte Count Registers (TBCR0, 1). When the SNIC receives a command to transmit the packet pointed to by these registers, buffer memory data will be moved into the FIFO as required during transmission. The SNIC will generate and append the preamble, synch and CRC fields.

General Transmit Packet Format

Transmit Destination Address 6 Bytes

Byte Source Address 6 Bytes

Count Type/Length 2 Bytes

TBCR0, 1

Data

Pad (If Datak46 Bytes)

TRANSMIT PACKET ASSEMBLY

The SNIC requires a contiguous assembled packet with the format shown. The transmit byte count includes the Destination Address, Source Address, Length Field and Data. It does not include preamble and CRC. When transmitting data smaller than 46 bytes, the packet must be padded to a minimum size of 64 bytes. The programmer is responsible for adding and stripping pad bytes.

TRANSMISSION

Prior to transmission, the TPSR (Transmit Page Start Register) and TBCR0, TBCR1 (Transmit Byte Count Registers) must be initialized. To initiate transmission of the packet the TXP bit in the Command Register is set. The Transmit Status Register (TSR) is cleared and the SNIC begins to prefetch transmit data from memory (unless the SNIC is currently receiving). If the interframe gap has timed out the SNIC will begin transmission.

CONDITIONS REQUIRED TO BEGIN TRANSMISSION

In order to transmit a packet, the following three conditions must be met:

1. The Interframe Gap Timer has timed out the first 6.4 ms of the Interframe Gap.

2. At least one byte has entered the FIFO. (This indicates that the burst transfer has been started.)

3. If a collision had been detected then before transmission the packet time must have timed out.

In typical systems the SNIC prefetchs the first burst of bytes before the 6.4 m s timer expires. The time during which SNIC transmits preamble can also be used to load the FIFO.

Note: If carrier sense is asserted before a byte has been loaded into the

FIFO, the SNIC will become a receiver.

COLLISION RECOVERY

During transmission, the Buffer Management logic monitors the transmit circuitry to determine if a collision has occurred. If a collision is detected, the Buffer Management logic will reset the FIFO and restore the Transmit DMA pointers for retransmission of the packet. The COL bit will be set in the TSR and the NCR (Number of Collisions Register) will be incremented. If 15 retransmissions each result in a collision the transmission will be aborted and the ABT bit in the TSR will be set.

Note: NCR reads as zeroes if excessive collisions are encountered.

46 Bytes

TRANSMIT PACKET ASSEMBLY FORMAT

The following diagrams describe the format for how packets must be assembled prior to transmission for different byte ordering schemes. The various formats are selected in the Data Configuration Register.

D15 D8 D7 D0

Destination Address 1 Destination Address 0

Destination Address 3 Destination Address 2

Destination Address 5 Destination Address 4

Source Address 1 Source Address 0

Source Address 3 Source Address 2

Source Address 5 Source Address 4

Type/Length 1 Type/Length 0

Data 1 Data 0

BOSe0, WTSe1 in Data Configuration Register.

This format is used with Series 32xxx, or 808xx processors.

D15 D8 D7 D0

Destination Address 0 Destination Address 1

Destination Address 2 Destination Address 3

Destination Address 4 Destination Address 5

Source Address 0 Source Address 1

Source Address 2 Source Address 3

Source Address 4 Source Address 5

Type/Length 0 Type/Length 1

Data 0 Data 1

BOSe1, WTSe1 in Data Configuration Register.

This format is used with 680x0 type processors.

D1 D0

Destination Address 0

Destination Address 1

Destination Address 2

Destination Address 3

Destination Address 4

Destination Address 5

Source Address 0

Source Address 1

Source Address 2

Source Address 3

Source Address 4

Source Address 5

BOSe0, WTSe0 in Data Configuration Register.

This format is used with general 8-bit processors.

Note: All examples above will result in a transmission of a packet in order of

DA0, DA1, DA3 . . . bits within each byte will be transmitted least significant bit first.

Destination Address.

Page 19

9.0 Remote DMA

The Remote DMA channel is used to both assemble packets for transmission, and to remove received packets from the Receive Buffer Ring. It may also be used as a general purpose slave DMA channel for moving blocks of data or commands between host memory and local buffer memory. There are three modes of operation, Remote Write, Remote Read, or Send Packet.

Two register pairs are used to control the Remote DMA, a Remote Start Address (RSAR0, RSAR1) and a Remote Byte Count (RBCR0, RBCR1) register pair. The Start Address Register pair points to the beginning of the block to be moved while the Byte Count Register pair is used to indicate the number of bytes to be transferred. Full handshake logic is provided to move data between local buffer memory and a bidirectional I/O port.

REMOTE WRITE

A Remote Write transfer is used to move a block of data from the host into local buffer memory. The Remote DMA will read data from the I/O port and sequentially write it to local buffer memory beginning at the Remote Start Address. The DMA Address will be incremented and the Byte Counter will be decremented after each transfer. The DMA is terminated when the Remote Byte Count Register reaches a count of zero.

REMOTE READ

A Remote Read transfer is used to move a block of data from local buffer memory to the host. The Remote DMA will

Remote DMA Autoinitialization from Buffer Ring

sequentially read data from the local buffer memory, beginning at the Remote Start Address, and write data to the I/O port. The DMA Address will be incremented and the Byte Counter will be decremented after each transfer. The DMA is terminated when the Remote Byte Count Register reaches zero.

SEND PACKET COMMAND

The Remote DMA channel can be automatically initialized to transfer a single packet from the Receive Buffer Ring. The CPU begins this transfer by issuing a ‘‘Send Packet’’ Command. The DMA will be initialized to the value of the Boundary Pointer Register and the Remote Byte Count Register pair (RBCR0, RBCR1) will be initialized to the value of the Receive Byte Count fields found in the Buffer Header of each packet. After the data is transferred, the Boundary Pointer is advanced to allow the buffers to be used for new receive packets. The Remote Read will terminate when the Byte Count equals zero. The Remote DMA is then prepared to read the next packet from the Receive Buffer Ring. If the DMA pointer crosses the Page Stop Register, it is reset to the Page Start Address. This allows the Remote DMA to remove packets that have wrapped around to the top of the Receive Buffer Ring.

Note 1: In order for the SNIC to correctly execute the Send Packet Com-

mand, the upper Remote Byte Count Register (RBCR1) must first be loaded with 0FH.

Note 2: The Send Packet command cannot be used with 680x0 type proc-

essors.

TL/F/10469– 15

Page 20

10.0 Internal Registers

All registers are 8-bit wide and mapped into four pages which are selected in the Command Register (PS0, PS1). Pins RA0 – RA3 are used to address registers within each page. Page 0 registers are those registers which are com-

10.1 REGISTER ADDRESS MAPPING

10.2 REGISTER ADDRESS ASSIGNMENTS

Page 0 Address Assignments (PS1e0, PS0e0)

RA0–RA3 RD WR

00H Command (CR) Command (CR)

01H Current Local DMA Page Start Register

Address 0 (CLDA0) (PSTART)

02H Current Local DMA Page Stop Register

Address 1 (CLDA1) (PSTOP)

03H Boundary Pointer Boundary Pointer

(BNRY) (BNRY)

04H Transmit Status Transmit Page Start

05H Number of Collisions Transmit Byte Count

06H FIFO (FIFO) Transmit Byte Count

07H Interrupt Status Interrupt Status

08H Current Remote DMA Remote Start Address

Address 0 (CRDA0) Register 0 (RSAR0)

monly accessed during SNIC operation while page 1 registers are used primarily for initialization. The registers are partitioned to avoid having to perform two write/read cycles to access commonly used registers.

TL/F/10469– 16

RA0–RA3 RD WR

09H Current Remote DMA Remote Start Address

Address 1 (CRDA1) Register 1 (RSAR1)

0AH Reserved Remote Byte Count

0BH Reserved Remote Byte Count

0CH Receive Status Receive Configuration

0DH Tally Counter 0 Transmit Configuration

(Frame Alignment Register (TCR) Errors) (CNTR0)

0EH Tally Counter 1 Data Configuration

(CRC Errors) Register (DCR) (CNTR1)

0FH Tally Counter 2 Interrupt Mask

Missed Packet Register (IMR) Errors) (CNTR2)

Page 21

10.0 Internal Registers (Continued)

Page 1 Address Assignments (PS1

RA0–RA3 RD WR

00H Command (CR) Command (CR)

01H Physical Address Physical Address

02H Physical Address Physical Address

03H Physical Address Physical Address

04H Physical Address Physical Address

05H Physical Address Physical Address

06H Physical Address Physical Address

07H Current Page Current Page

08H Multicast Address Multicast Address

09H Multicast Address Multicast Address

0AH Multicast Address Multicast Address

0BH Multicast Address Multicast Address

0CH Multicast Address Multicast Address

0DH Multicast Address Multicast Address

0EH Multicast Address Multicast Address

0FH Multicast Address Multicast Address

0, PS0e1)

Page 2 Address Assignments (PS1e1, PS0e0)

RA0–RA3 RD WR

00H Command (CR) Command (CR)

01H Page Start Register Current Local DMA

(PSTART) Address 0 (CLDA0)

02H Page Stop Register Current Local DMA

(PSTOP) Address 1 (CLDA1)

03H Remote Next Packet Remote Next Packet

Pointer Pointer

04H Transmit Page Start Reserved

Address (TPSR)

05H Local Next Packet Local Next Packet

Pointer Pointer

06H Address Counter Address Counter

(Upper) (Upper)

07H Address Counter Address Counter

(Lower) (Lower)

08H Reserved Reserved

09H Reserved Reserved

0AH Reserved Reserved

0BH Reserved Reserved

0CH Receive Configuration Reserved

0DH Transmit Reserved

Configuration Register (TCR)

0EH Data Configuration Reserved

0FH Interrupt Mask Reserved

Note: Page 2 registers should only be accessed for diagnostic purposes.

They should not be modified during normal operation.

Page 3 should never be modified.

Page 22

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS

COMMAND REGISTER (CR) 00H (READ/WRITE)

The Command Register is used to initiate transmissions, enable or disable Remote DMA operations and to select register pages. To issue a command the microprocessor sets the corresponding bit(s) (RD2, RD1, RD0, TXP). Further commands may be overlapped, but with the following rules: (1) If a transmit command overlaps with a remote DMA operation, bits RD0, RD1, and RD2 must be maintained for the remote DMA command when setting the TXP bit. Note, if a remote DMA command is re-issued when giving the transmit command, the DMA will complete immediately if the remote byte count register has not been reinitialized. (2) If a remote DMA operation overlaps a transmission, RD0, RD1, and RD2 may be written with the desired values and a ‘‘0’’ written to the TXP bit. Writing a ‘‘0’’ to this bit has no effect. (3) A remote write DMA may not overlap remote read operation or visa versa. Either of these operations must either complete or be aborted before the other operation may start. Bits PS1, PS0, RD2, and STP may be set any time.

76543210

PS1 PS0 RD2 RD1 RD0 TXP STA STP

Bit Symbol Description

D0 STP Stop: Software reset command, takes the controller offline, no packets will be received or transmitted. Any

D1 STA Start: This bit is used to activate the SNIC after either power up, or when the SNIC has been placed in a

D2 TXP Transmit Packet: This bit must be set to initiate transmission of a packet. TXP is internally reset either after

D3, RD0, Remote DMA Command: These three encoded bits control operation of the Remote DMA channel. RD2 D4, RD1, and and

D5 RD2

D6 PS0 Page Select: These two encoded bits select which register page is to be accessed with addresses RA0 –3.

and and PS1 PS0

D7 PS1 0 0 Register Page 0

reception or transmission in progress will continue to completion before entering the reset state. To exit this state, the STP bit must be reset and the STA bit must be set high. To perform a software reset, this bit should be set high. The software reset has executed only when indicated by the RST bit in the ISR being set to 1. STP powers up high.

Note: If the SNIC has previously been in start mode and the STP is set, both the STP and STA bits will remain set.

reset mode by software command or error. STA powers up low.

the transmission is completed or aborted. This bit should be set only after the Transmit Byte Count and Transmit Page Start registers have been programmed.

can be set to abort any Remote DMA command in progress. The Remote Byte Count Registers should be cleared when a Remote DMA has been aborted. The Remote Start Addresses are not restored to the starting address if the Remote DMA is aborted.

RD2 RD1 RD0

0 0 0 Not Allowed 0 0 1 Remote Read 0 1 0 Remote Write (Note 2) 0 1 1 Send Packet 1 X X Abort/Complete Remote DMA (Note 1)

Note 1: If a remote DMA operation is aborted and the remote byte count has not decremented to zero. PRQ will remain high. A read acknowledge (RACK) on a write acknowledge (WACK) will reset PRQ low.

Note 2: For proper operation of the Remote Write DMA, there are two steps which must be performed before using the Remote Write DMA. The steps are as follows:

I) Write a non-zero value into RBCR0.

II) Set bits RD2, RD1, and RD0 to 0, 0, and 1.

III) Issue the Remote Write DMA Command (RD2, RD1, RD0

0, 1, 0).

0 1 Register Page 1 1 0 Register Page 2 1 1 Reserved

Page 23

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

INTERRUPT STATUS REGISTER (ISR) 07H (READ/WRITE)

This register is accessed by the host processor to determine the cause of an interrupt. Any interrupt can be masked in the Interrupt Mask Register (IMR). Individual interrupt bits are cleared by writing a ‘‘1’’ into the corresponding bit of the ISR. The INT signal is active as long as any unmasked signal is set, and will not go low until all unmasked bits in this register have been cleared. The ISR must be cleared after power up by writing it with all 1’s.

765 43210

RST RDC CNT OVW TXE RXE PTX PRX

Bit Symbol Description

D0 PRX Packet Received: Indicates packet received with no errors.

D1 PTX Packet Transmitted: Indicates packet transmitted with no errors.

D2 RXE Receive Error: Indicates that a packet was received with one or more of the following errors:

D3 TXE Transmit Error: Set when packet transmitted with one or more of the following errors:

D4 OVW Overwrite Warning: Set when receive buffer ring storage resources have been exhausted.

D5 CNT Counter Overflow: Set when MSB of one or more of the Network Tally Counters has been set.

D6 RDC Remote DMA Complete: Set when Remote DMA operation has been completed.

D7 RST Reset Status: Set when SNIC enters reset state and cleared when a Start Command is issued to

Ð CRC Error Ð Frame Alignment Error Ð FIFO Overrun Ð Missed Packet

Ð Excessive Collisions Ð FIFO Underrun

(Local DMA has reached Boundary Pointer)

the CR. This bit is also set when a Receive Buffer Ring overflow occurs and is cleared when one or more packets have been removed from the ring. Writing to this bit has no effect.

Note: This bit does not generate an interrupt, it is merely a status indicator.

Page 24

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

INTERRUPT MASK REGISTER (IMR) 0FH (WRITE)

The Interrupt Mask Register is used to mask interrupts. Each interrupt mask bit corresponds to a bit in the Interrupt Status Register (ISR). If an interrupt mask bit is set, an interrupt will be issued whenever the corresponding bit in the ISR is set. If any bit in the IMR is set low, an interrupt will not occur when the bit in the ISR is set. The IMR powers up to all zeroes.

76543210

Ð RDCE CNTE OVWE TXEE RXEE PTXE PRXE

Bit Symbol Description

D0 PRXE Packet Received Interrupt Enable

D1 PTXE Packet Transmitted Interrupt Enable

D2 RXEE Receive Error Interrupt Enable

D3 TXEE Transmit Error Interrupt Enable

D4 OVWE Overwrite Warning Interrupt Enable

D5 CNTE Counter Overflow Interrupt Enable

D6 RDCE DMA Complete Interrupt Enable

D7 Reserved Reserved

0: Interrupt Disabled 1: Enables Interrupt when packet received

0: Interrupt Disabled 1: Enables Interrupt when packet is transmitted

0: Interrupt Disabled 1: Enables Interrupt when packet received with error

0: Interrupt Disabled 1: Enables Interrupt when packet transmission results in error

0: Interrupt Disabled 1: Enables Interrupt when Buffer Management Logic lacks sufficient buffers to store incoming packet

0: Interrupt Disabled 1: Enables Interrupt when MSB of one or more of the Network Statistics counters has been set

0: Interrupt Disabled 1: Enables Interrupt when Remote DMA transfer has been completed

Page 25

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

DATA CONFIGURATION REGISTER (DCR) 0EH (WRITE)

This Register is used to program the SNIC for 8- or 16-bit memory interface, select byte ordering in 16-bit applications and establish FIFO thresholds. The DCR must be initialized prior to loading the Remote Byte Count Registers. LAS is set on

power up.

76543210

Ð FT1 FT0 ARM LS LAS BOS WTS

Bit Symbol Description

D0 WTS Word Transfer Select

D1 BOS Byte Order Select

D2 LAS Long Address Select

D3 LS Loopback Select

D4 ARM Auto-Initialize Remote

D5 FT0 FIFO Threshold Select: Encoded FIFO threshold. Establishes point at which bus is requested when filling or

and and

D6 FT1

0: Selects byte-wide DMA transfers 1: Selects word-wide DMA transfers

; WTS establishes byte or word transfers for both Remote and Local DMA transfers

Note: When word-wide mode is selected up to 32k words are addressable; A0 remains low.

0: MS byte placed on AD15–AD8 and LS byte on AD7 –AD0. (32xxx, 80x86) 1: MS byte placed on AD7–AD0 and LS byte on AD15 –A8. (680x0)

: Ignored when WTS is low

0: Dual 16-bit DMA mode 1: Single 32-bit DMA mode

; When LAS is high, the contents of the Remote DMA registers RSAR0, 1 are issued as A16–A31 Power up high

0: Loopback mode selected. Bits D1 and D2 of the TCR must also be programmed for Loopback operation 1: Normal Operation

0: Send Command not executed, all packets removed from Buffer Ring under program control 1: Send Command executed, Remote DMA auto-initialized to remove packets from Buffer Ring

Note: Send Command cannot be used with 680x0 byte processors.

emptying the FIFO. During reception, the FIFO threshold indicates the number of bytes (or words) the FIFO has filled serially from the network before bus request (BREQ) is asserted.

Note: FIFO threshold setting determines the DMA burst length.

Receive Thresholds

FT1 FT0 Word Wide Byte Wide

0 0 1 Word 2 Bytes 0 1 2 Words 4 Bytes 1 0 4 Words 8 Bytes 1 1 6 Words 12 Bytes

During transmission, the FIFO threshold indicates the number of bytes (or words) the FIFO has filled from the Local DMA before BREQ is asserted. Thus, the transmission threshold is 13 bytes less the received threshold.

Page 26

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

TRANSMIT CONFIGURATION REGISTER (TCR) 0DH (WRITE)

The transmit configuration establishes the actions of the transmitter section of the SNIC during transmission of a packet on the network. LB1 and LB0 which select loopback mode power up as 0.

76543210

Ð Ð Ð OFST ATD LB1 LB0 CRC

Bit Symbol Description

D0 CRC Inhibit CRC

D1 LB0 Encoded Loopback Control: These encoded configuration bits set the type of loopback that is to be

and and

D2 LB1

D3 ATD Auto Transmit Disable: This bit allows another station to disable the SNIC’s transmitter by transmission of a

D4 OFST Collision Offset Enable: This bit modifies the backoff algorithm to allow prioritization of nodes.

D5 Reserved Reserved

D6 Reserved Reserved

D7 Reserved Reserved

0: CRC appended by transmitter 1: CRC inhibited by transmitter In loopback mode CRC can be enabled or disabled to test the CRC logic

performed. Note that loopback in mode 2 places the ENDEC Module in loopback mode and that D3 of the DCR must be set to zero for loopback operation.

Mode 0 0 0 Normal Operation (LPBK Mode 1 0 1 Internal NIC Module Loopback (LPBK Mode 2 1 0 Internal ENDEC Module Loopback (LPBK Mode 3 1 1 External Loopback (LPBK

particular multicast packet. The transmitter can be re-enabled by resetting this bit or by reception of a second particular multicast packet.

1: Reception of multicast address hashing to bit 62 disables transmitter, reception of multicast address hashing to bit 63 enables transmitter.

0: Backoff Logic implements normal algorithm. 1: Forces Backoff algorithm modification to 0 to 2 standard backoff. (For the first three collisions, the station has higher average backoff delay making a low

priority mode.)

LB1 LB0

min(3an, 10)

slot times for first three collisions, then follows

Page 27

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

TRANSMIT STATUS REGISTER (TSR) 04H (READ)

This register records events that occur on the media during transmission of a packet. It is cleared when the next transmission is initiated by the host. All bits remain low unless the event that corresponds to a particular bit occurs during transmission. Each transmission should be followed by a read of this register. The contents of this register are not specified until after the first transmission.

76543210

OWC CDH FU CRS ABT COL Ð PTX

Bit Symbol Description

D0 PTX Packet Transmitted: Indicates transmission without error. (No excessive collisions or FIFO

underrun) (ABT

D1 Reserved Reserved

D2 COL Transmit Collided: Indicates that the transmission collided at least once with another station on

the network. The number of collisions is recorded in the Number of Collisions Registers (NCR).

D3 ABT Transmit Aborted: Indicates the SNIC aborted transmission because of excessive collisions.

(Total number of transmissions including original transmission attempt equals 16.)

D4 CRS Carrier Sense Lost: This bit is set when carrier is lost during transmission of the packet.

Transmission is not aborted on loss of carrier.

D5 FU FIFO Underrun: If the SNIC cannot gain access of the bus before the FIFO empties, this bit is

set. Transmission of the packet will be aborted.

D6 CDH CD Heartbeat: Failure of the transceiver to transmit a collision signal after transmission of a

packet will set this bit. The Collision Detect (CD) heartbeat signal must commence during the first

6.4 ms of the Interframe Gap following a transmission. In certain collisions, the CD Heartbeat bit will be set even though the transceiver is not performing the CD heartbeat test.

D7 OWC Out of Window Collision: Indicates that a collision occurred after a slot time (51.2 ms).

Transmissions rescheduled as in normal collisions.

‘‘0’’, FUe‘‘0’’)

Page 28

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

RECEIVE CONFIGURATION REGISTER (RCR) 0CH (WRITE)

This register determines operation of the SNIC during reception of a packet and is used to program what types of packets to accept.

76543210

Ð Ð MON PRO AM AB AR SEP

Bit Symbol Description

D0 SEP Save Errored Packets

D1 AR Accept Runt Packets: This bit allows the receiver to accept packets that are smaller than 64

D2 AB Accept Broadcast: Enables the receiver to accept a packet with an all 1’s destination address.

D3 AM Accept Multicast: Enables the receiver to accept a packet with a multicast address, all multicast

D4 PRO Promiscuous Physical: Enables the receiver to accept all packets with a physical address.

D5 MON Monitor Mode: Enables the receiver to check addresses and CRC on incoming packets without

D6 Reserved Reserved

D7 Reserved Reserved

Note: D2 and D3 are ‘‘OR’d’’ together, i.e., if D2 and D3 are set the SNIC will accept broadcast and multicast addresses as well as its own physical address. To establish full promiscuous mode, bits D2, D3, and D4 should be set. In addition the multicast hashing array must be set to all 1’s in order to accept all multicast addresses.

0: Packets with receive errors are rejected. 1: Packets with receive errors are accepted. Receive errors are CRC and Frame Alignment

errors.

bytes. The packet must be at least 8 bytes long to be accepted as a runt. 0: Packets with fewer than 64 bytes rejected. 1: Packets with fewer than 64 bytes accepted.

0: Packets with broadcast destination address rejected. 1: Packets with broadcast destination address accepted.

addresses must pass the hashing array. 0: Packets with multicast destination address not checked. 1: Packets with multicast destination address checked.

0: Physical address of node must match the station address programmed in PAR0–PAR5. 1: All packets with physical addresses accepted.

buffering to memory. The Missed Packet Tally counter will be incremented for each recognized packet.

0: Packets buffered to memory. 1: Packets checked for address match, good CRC and Frame Alignment but not buffered to

memory.

Page 29

10.0 Internal Registers (Continued)

10.3 REGISTER DESCRIPTIONS (Continued)

RECEIVE STATUS REGISTER (RSR) 0CH (READ)

This register records status of the received packet, including information on errors and the type of address match, either physical or multicast. The contents of this register are written to buffer memory by the DMA after reception of a good packet. If packets with errors are to be saved the receive status is written to memory at the head of the erroneous packet if an erroneous packet is received. If packets with errors are to be rejected the RSR will not be written to memory. The contents will be cleared when the next packet arrives. CRC errors, Frame Alignment errors and missed packets are counted internally by the SNIC which relinguishes the Host from reading the RSR in real time to record errors for Network Management Functions. The contents of this register are not specified until after the first reception.

76543210

DFR DIS PHY MPA FO FAE CRC PRX

Bit Symbol Description

D0 PRX Packet Received Intact: Indicates packet received without error. (Bits CRC, FAE, FO, and MPA

D1 CRC CRC Error: Indicates packet received with CRC error. Increments Tally Counter (CNTR1). This

D2 FAE Frame Alignment Error: Indicates that the incoming packet did not end on a byte boundary and

D3 FO FIFO Overrun: This bit is set when the FIFO is not serviced causing overflow during reception.

D4 MPA Missed Packet: Set when a packet intended for node cannot be accepted by SNIC because of a

D5 PHY Physical/Multicast Address: Indicates whether received packet had a physical or multicast

D6 DIS Receiver Disabled: Set when receiver disabled by entering Monitor mode. Reset when receiver

D7 DFR Deferring: Set when internal Carrier Sense or Collision signals are generated in the ENDEC

Note: Following coding applies to CRC and FAE bits.

FAE CRC Type of Error

0 0 No Error (Good CRC and 0 1 CRC Error 1 0 Illegal, Will Not Occur 1 1 Frame Alignment Error and CRC Error

are zero for the received packet.)

bit will also be set for Frame Alignment errors.

the CRC did not match at last byte boundary. Increments Tally Counter (CNTR0).

Reception of the packet will be aborted.

lack of receive buffers or if the controller is in monitor mode and did not buffer the packet to memory. Increments Tally Counter (CNTR2).

address type. 0: Physical Address Match 1: Multicast/Broadcast Address Match

is re-enabled when exiting Monitor mode.

module. If the transceiver has asserted the CD line as a result of the jabber, this bit will stay set indicating the jabber condition.

6 Dribble Bits)

Page 30

10.0 Internal Registers (Continued)

10.4 DMA REGISTERS

The DMA Registers are partitioned into groups; Transmit, Receive and Remote DMA Registers. The Transmit registers are used to initialize the Local DMA Channel for transmission of packets while the Receive Registers are used to initialize the Local DMA Channel for packet Reception. The Page Stop, Page Start, Current and Boundary Registers are used by the Buffer Management Logic to supervise the Receive Buffer Ring. The Remote DMA Registers are used to initialize the Remote DMA.

Note: In the figure above, registers are shown as 8 or 16 bits wide. Although

some registers are 16-bit internal registers, all registers are accessed as 8-bit registers. Thus the 16-bit Transmit Byte Count Register is broken into two 8-bit registers, TBCR0, TBCR1. Also TPSR, PSTART, PSTOP, CURR and BNRY only check or control the upper 8 bits of address information on the bus. Thus, they are shifted to positions 15– 8 in the diagram above.

10.5 TRANSMIT DMA REGISTERS

TRANSMIT PAGE START REGISTER (TPSR)

This register points to the assembled packet to be transmitted. Only the eight higher order addresses are specified since all transmit packets are assembled on 256-byte page boundaries. The bit assignment is shown below. The values placed in bits D7 –D0 will be used to initialize the higher order address (A8 – A15) of the Local DMA for transmission. The lower order bits (A7–A0) are initialized to zero.

DMA Registers

TL/F/10469– 17

Bit Assignment

76543210

TPSR A15 A14 A13 A12 A11 A10 A9 A8

(A7– A0 Initialized to Zero)

TRANSMIT BYTE COUNT REGISTER 0, 1 (TBCR0, TBCR1)

These two registers indicate the length of the packet to be transmitted in bytes. The count must include the number of bytes in the source, destination, length and data fields. The maximum number of transmit bytes allowed is 64 Kbytes. The SNIC will not truncate transmissions longer than 1500 bytes. The bit assignment is shown below:

76543210

TBCR1 L15 L14 L13 L12 L11 L10 L9 L8

76543210

TBCR0 L7 L6 L5 L4 L3 L2 L1 L0

Page 31

10.0 Internal Registers (Continued)

10.6 LOCAL DMA RECEIVE REGISTERS

PAGE START AND STOP REGISTERS (PSTART, PSTOP)

The Page Start and Page Stop Registers program the starting and stopping address of the Receive Buffer Ring. Since the SNIC uses fixed 256-byte buffers aligned on page boundaries only the upper 8 bits of the start and stop address are specified.

PSTART, PSTOP Bit Assignment

PSTART, PSTOP

BOUNDARY (BNRY) REGISTER

This register is used to prevent overflow of the Receive Buffer Ring. Buffer management compares the contents of this register to the next buffer address when linking buffers together. If the contents of this register match the next buffer address the Local DMA operation is aborted.

BNRY A15 A14 A13 A12 A11 A10 A9 A8

CURRENT PAGE REGISTER (CURR)

This register is used internally by the Buffer Management Logic as a backup register for reception. CURR contains the address of the first buffer to be used for a packet reception and is used to restore DMA pointers in the event of receive errors. This register is initialized to the same value as PSTART and should not be written to again unless the controller is Reset.

CURR A15 A14 A13 A12 A11 A10 A9 A8

CURRENT LOCAL DMA REGISTER 0,1 (CLDA0, 1)

These two registers can be accessed to determine the current local DMA address.

CLDA1 A15 A14 A13 A12 A11 A10 A9 A8

CLDA0 A7 A6 A5 A4 A3 A2 A1 A0

10.7 REMOTE DMA REGISTERS

REMOTE START ADDRESS REGISTERS (RSAR0, 1)

Remote DMA operations are programmed via the Remote Start Address (RSAR0, 1) and Remote Byte Count (RBCR0, 1) registers. The Remote Start Address is used to point to the start of the block of data to be transferred and the Remote Byte Count is used to indicate the length of the block (in bytes).

RSAR1 A15 A14 A13 A12 A11 A10 A9 A8

76543210

A15 A14 A13 A12 A11 A10 A9 A8

76543210

REMOTE BYTE COUNT REGISTERS (RBCR0, 1)

76543210

RBCR1 BC15 BC14 BC13 BC12 BC11 BC10 BC9 BC8

76543210

RBCR0 BC7 BC6 BC5 BC4 BC3 BC2 BC1 BC0

Note: RSAR0 programs the start address bits A0– A7.

RSAR1 programs the start address bits A8 –A15. Address incremented by two for word transfers, and by one for byte transfers. Byte Count decremented by two for word transfers and by one for byte transfers. RBCR0 programs LSB byte count. RBCR1 programs MSB byte count.

CURRENT REMOTE DMA ADDRESS (CRDA0, CRDA1)

The Current Remote DMA Registers contain the current address of the Remote DMA. The bit assignment is shown below:

76543210

CRDA1 A15 A14 A13 A12 A11 A10 A9 A8

76543210

CRDA0 A7 A6 A5 A4 A3 A2 A1 A0

10.8 PHYSICAL ADDRESS REGISTERS (PAR0–PAR5)

The physical address registers are used to compare the destination address of incoming packets for rejecting or accepting packets. Comparisons are performed on a bytewide basis. The bit assignment shown below relates the sequence in PAR0 –PAR5 to the bit sequence of the received packet.

D7 D6 D5 D4 D3 D2 D1 D0

PAR0 DA7 DA6 DA5 DA4 DA3 DA2 DA1 DA0

PAR1 DA15 DA14 DA13 DA12 DA11 DA10 DA9 DA8

PAR2 DA23 DA22 DA21 DA20 DA19 DA18 DA17 DA16

PAR3 DA31 DA30 DA29 DA28 DA27 DA26 DA25 DA24

PAR4 DA39 DA38 DA37 DA36 DA35 DA34 DA33 DA32

PAR5 DA47 DA46 DA45 DA44 DA43 DA42 DA41 DA40

Destination Address Source

P/S DA0 DA1 DA2 DA3 . . . DA46 DA47 SA0 . . .

Note: P/SePreamble, Synch

Physical/Multicast Bit

DA0

10.9 MULTICAST ADDRESS REGISTERS (MAR0–MAR7)

The multicast address registers provide filtering of multicast addresses hashed by the CRC logic. All destination addresses are fed through the CRC logic and as the last bit of the destination address enters the CRC, the 6 most signifi-

76543210

RSAR0 A7 A6 A5 A4 A3 A2 A1 A0

Page 32

10.0 Internal Registers (Continued)

cant bits of the CRC generator are latched. These 6 bits are then decoded bya1of64decode to index a unique filter bit (FB0–63) in the multicast address registers. If the filter bit selected is set, the multicast packet is accepted. The system designer would use a program to determine which filter bits to set in the multicast registers. All multicast filter bits that correspond to multicast address accepted by the node are then set to one. To accept all multicast packets all of the registers are set to all ones.

Note: Although the hashing algorithm does not guarantee perfect filtering of

multicast address, it will perfectly filter up to 64 multicast addresses if these addresses are chosen to map into unique locations in the multicast filter.

TL/F/10469– 18

D7 D6 D5 D4 D3 D2 D1 D0

MAR0 FB7 FB6 FB5 FB4 FB3 FB2 FB1 FB0

MAR1 FB15 FB14 FB13 FB12 FB11 FB10 FB9 FB8

MAR2 FB23 FB22 FB21 FB20 FB19 FB18 FB17 FB16

MAR3 FB31 FB30 FB29 FB28 FB27 FB26 FB25 FB24

MAR4 FB39 FB38 FB37 FB36 FB35 FB34 FB33 FB32

MAR5 FB47 FB46 FB45 FB44 FB43 FB42 FB41 FB40

MAR6 FB55 FB54 FB53 FB52 FB51 FB50 FB49 FB48

MAR7 FB63 FB62 FB61 FB60 FB59 FB58 FB57 FB56

If address Y is found to hash to the value 32 (20H), then FB32 in MAR4 should be initialized to ‘‘1’’. This will cause the SNIC to accept any multicast packet with the address Y.

10.10 NETWORK TALLY COUNTERS

Three 8-bit counters are provided for monitoring the number of CRC errors, Frame Alignment Errors and Missed Packets. The maximum count reached by any counter is 192 (C0H). These registers will be cleared when read by the CPU. The count is recorded in binary in CT0 – CT7 of each Tally Register.

Frame Alignment Error Tally (CNTR0)

This counter increments every time a packet is received with a Frame Alignment Error. The packet must have been recognized by the address recognition logic. The counter is cleared after it is read by the processor.

76543210

CNTR0 CT7 CT6 CT5 CT4 CT3 CT2 CT1 CT0

CRC Error Tally (CNTR1)

This counter is incremented every time a packet is received with a CRC error. The packet must first be recognized by the address recognition logic. The counter is cleared after it is read by the processor.

76543210

CNTR1 CT7 CT6 CT5 CT4 CT3 CT2 CT1 CT0

Frames Lost Tally Register (CNTR2)

This counter is incremented if a packet cannot be received due to lack of buffer resources. In monitor mode, this counter will count the number of packets that pass the address recognition logic.

76543210

CNTR2 CT7 CT6 CT5 CT4 CT3 CT2 CT1 CT0

FIFO

This is an 8-bit register that allows the CPU to examine the contents of the FIFO after loopback. The FIFO will contain the last 8 data bytes transmitted in the loopback packet. Sequential reads from the FIFO will advance a pointer in the FIFO and allow reading of all 8 bytes.

76543210

FIFO DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0

Note: The FIFO should only be read when the SNIC has been programmed

in loopback mode.

NUMBER OF COLLISIONS (NCR)

This register contains the number of collisions a node experiences when attempting to transmit a packet. If no collisions are experienced during a transmission attempt, the COL bit of the TSR will not be set and the contents of NCR will be zero. If there are excessive collisions, the ABT bit in the TSR will be set and the contents of NCR will be zero. The NCR is cleared after the TXP bit in the CR is set.

76543210

NCR Ð Ð Ð Ð NC3 NC2 NC1 NC0

Page 33

11.0 Initialization Procedures

The SNIC must be initialized prior to transmission or reception of packets from the network. Power on reset is applied to the SNIC’s reset pin. This clears/sets the following bits:

Command Register (CR) TXP, STA RD2, STP

Interrupt Status (ISR) RST

Interrupt Mask (IMR) All Bits

Data Control (DCR) LAS

Transmit Config. (TCR) LB1, LB0

The SNIC remains in its reset state until a Start Command is issued. This guarantees that no packets are transmitted or received and that the SNIC remains a bus slave until all appropriate internal registers have been programmed. After initialization the STP bit of the command register is reset and packets may be received and transmitted.

Initialization Sequence

The following initialization procedure is mandatory.

1. Program Command Register for Page 0 (Command

2. Initialize Data Configuration Register (DCR)

3. Clear Remote Byte Count Registers (RBCR0, RBCR1)

4. Initialize Receive Configuration Register (RCR)

5. Place the SNIC in LOOPBACK mode 1 or 2 (Transmit

6. Initialize Receive Buffer Ring: Boundary Pointer

7. Clear Interrupt Status Register (ISR) by writing 0FFH to

8. Initialize Interrupt Mask Register (IMR)

9. Program Command Register for page 1 (Command

10. Put SNIC in START mode (Command Registere22H).

11. Initialize the Transmit Configuration for the intended val-

Before receiving packets, the user must specify the location of the Receive Buffer Ring. This is programmed in the Page Start and Page Stop Registers. In addition, the Boundary and Current Page Register must be initialized to the value of the Page Start Register. These registers will be modified during reception of packets.

Configuration Register

21H)

02H or 04H)

(BNDRY), Page Start (PSTART), and Page Stop (PSTOP)

it.

61H)

I) Initialize Physical Address Registers (PAR0 –PAR5)

II) Initialize Multicast Address Registers (MAR0 –MAR5)

III) Initialize CURRent pointer

ue. The SNIC is now ready for transmission and reception.

12.0 Loopback Diagnostics

Three forms of local loopback are provided on the SNIC. The user has the ability to loopback through the deserializer on the controller, through the ENDEC module or the Coax Transceiver on the DP83901A SNIC. Because of the half

duplex architecture of the SNIC, loopback testing is a special mode of operation with the following restrictions:

Restrictions During Loopback

The FIFO is split into two halves, one used for transmission the other for reception. Only 8-bit fields can be fetched from memory so two tests are required for 16-bit systems to verify integrity of the entire data path. During loopback the maximum latency from the assertion of BREQ to BACK is 2.0 ms. Systems that wish to use the loopback test yet do not meet this latency can limit the loopback to 7 bytes without experiencing underflow. Only the last 8 bytes of the loopback packet are retained in the FIFO. The last 8 bytes can be read through the FIFO register which will advance through the FIFO to allow reading the receive packet sequentially.

Destination Addresse(6 Bytes) Station Physical Address

Source Address

Length 2 Bytes

Data

CRC Appended by SNIC

if CRC

When in word-wide mode with Byte Order Select set, the loopback packet must be assembled in the even byte location as shown below. (The loopback only operated with byte wide transfers.)

When in word-wide mode with Byte Order Select low, the following format must be used for the loopback packet.

46 to 1500 Bytes

‘‘0’’ in TCR

TL/F/10469– 50

Note: When using loopback in word mode 2n bytes must be programmed in

TBCR0, 1. Where n odd location.

actual number of bytes assembled in even or

TL/F/10469– 51

Page 34

12.0 Loopback Diagnostics (Continued)

To initiate a loopback the user first assembles the loopback packet then selects the type of loopback using the Transmit Configuration register bits LB0, LB1. The transmit configuration register must also be set to enable or disable CRC generation during transmission. The user then issues a normal transmit command to send the packet. During loopback the receiver checks for an address match and if CRC bit in the TCR is set, the receiver will also check the CRC. The last 8 bytes of the loopback packet are buffered and can read out of the FIFO using FIFO read port.

Loopback Modes

MODE 1: Loopback through the NIC Module (LB1

LB0

1): If this loopback is used, the NIC Modules’s serial-

izer is connected to the deserializer.

MODE 2: Loopback through the ENDEC Module (LB1

LB0

0): If the loopback is to be performed through the SNI, the SNIC provides a control (LPBK) that forces the ENDEC module to loopback all signals.

MODE 3: Loopback to Coax (LB1

1, LB0e1). Packets can be transmitted to the coax in loopback mode to check all of the transmit and receive paths and the coax itself.

Note: Collision and Carrier Sense can be generated by the ENDEC module

and are masked by the NIC module. It is not possible to go directly between the loopback modes, it is necessary to return to normal operation (00H) when changing modes.

Note: The FIFO may only be read during Loopback. Reading the FIFO at

any other time will cause the SNIC to malfunction.

Reading the Loopback Packet

The last 8 bytes of a received packet can be examined by 8 consecutive reads of the FIFO register. The FIFO pointer is incremented after the rising edge of the CPU’s read strobe by internally synchronizing and advancing the pointer. This may take up to four bus clock cycles, if the pointer has not been incremented by the time the CPU reads the FIFO register again, the SNIC will insert wait states.

Note: The FIFO may only be read during Loopback. Reading the FIFO at

any other time will cause the SNIC to malfunction.

Alignment of the Received Packet in the FIFO

Reception of the packet in the FIFO begins at location zero, after the FIFO pointer reaches the last location in the FIFO, the pointer wraps to the top of the FIFO overwriting the previously received data. This process continued until the last byte is received. The SNIC then appends the received byte count in the next two locations of the FIFO. The contents of the Upper Byte Count are also copied to the next FIFO location. The number of bytes used in the loopback packet determined the alignment of the packet in the FIFO.

The alignment for a 64-byte packet is shown below.

FIFO FIFO

Location Contents

0 Lower Byte Count First Byte Read

1 Upper Byte Count Second Byte Read

2 Upper Byte Count

3 Last Byte

4 CRC1

5 CRC2

6 CRC3

7 CRC4 Last Byte Read

For the following alignment in the FIFO the packet length should be (N x 8)

5 Bytes. Note that if the CRC bit in the TCR is set, CRC will not be appended by the transmitter. If the CRC is appended by the transmitter, the 1st four bytes, bytes N-3 to N, correspond to the CRC.

FIFO FIFO

Location Contents

0 Byte N-4 First Byte Read

1 Byte N-3 (CRC1) Second Byte Read

2 Byte N-2 (CRC2)

3 Byte N-1 (CRC3)

4 Byte N (CRC4)

5 Lower Byte Count

6 Upper Byte Count Last Byte Read

7 Upper Byte Count

LOOPBACK TESTS

Loopback capabilities are provided to allow certain tests to be performed to validate operation of the DP83901A SNIC prior to transmitting and receiving packets on a live network. Typically these tests may be performed during power up of a node. The diagnostic provides support to verify the following:

1. Verify integrity of data path. Received data is checked

against transmitted data.

2. Verify CRC logic’s capability to generate good CRC on

transmit, verify CRC on receive (good or bad CRC).

Page 35

12.0 Loopback Diagnostics (Continued)

3. Verify that the Address Recognition Logic can

a) Recognize address match packets

b) Reject packets that fail to match an address

LOOPBACK OPERATION IN THE SNIC

Loopback is a modified form of transmission using only half of the FIFO. This places certain restrictions on the use of loopback testing. When loopback mode is selected in the TCR, the FIFO is split. A packet should be assembled in memory with programming of TPSR and TBCR0, TBCR1 registers. When the transmit command is issued the following operations occur:

Transmitter Actions

1. Data is transferred from memory by the DMA until the FIFO is filled. For each transfer TBCR0 and TBCR1 are decremented. (Subsequent burst transfers are initiated when the number of bytes in the FIFO drops below the programmed threshold.)

2. The SNIC generates 56 bits of preamble followed by an 8-bit synch pattern.

3. Data transferred from FIFO to serializer.

4. If CRC

5. At end of Transmission PTX bit set in ISR.

Receiver Actions

1. Wait for synch, all preamble stripped.

2. Store packet in FIFO, increment receive byte count for

3. If CRC

4. At end of receive, receive byte count written into FIFO,

EXAMPLES

The following examples show what results can be expected from a properly operating SNIC during loopback. The restrictions and results of each type of loopback are listed for reference. The loopback tests are divided into two sets of tests. One to verify the data path, CRC generation and byte count through all three paths. The second set of tests uses internal loopback to verify the receiver’s CRC checking and address recognition. For all of the tests the DCR was programmed to 40H.

Note 1: Since carrier sense and collision detect are generated in the EN-

Note 2: CRC errors are always indicated by receiver if CRC is appended by

Note 3: Only the PTX bit in the ISR is set, the PRX bit is only set if status is

Note 4: All values are hex.

byte transmitted is the last byte from the FIFO (Allows software CRC to be appended). If CRC

1 in TCR, no CRC calculated by SNIC, the last

0, SNIC calcu-

lates and appends four bytes of CRC.

each incoming byte.

1 in TRC, receiver checks incoming packet for

CRC errors. If CRC

0 in TCR, receiver does not check CRC errors, CRC error bit always set in RSR (for address matching packets).

receive status register is updated. The PRX bit is typically set in the RSR even if the address does not match. If CRC errors are forced, the packet must match the address filters in order for the CRC error bit in the RSR to be set.

Path TCR RCR TSR RSR ISR

SNIC Internal 02 1F 53 02 02

(Note 1) (Note 2) (Note 3)

DEC module. They are blocked during NIC loopback, carrier and CD heartbeat are not seen and the CRS and CDH bits are set.

the transmitter.

written to memory. In loopback this action does not occur and the PRX bit remains 0 for all loopback modes.

Path TCR RCR TSR RSR ISR

SNIC Internal 04 1F 43 02 02

(Note 1)

Note 1: CDH is set, CRS is not set since it is generated by the external

encoder/decoder.

Path TCR RCR TSR RSR ISR

SNIC External 06 1F 03 02 02

(Note 1) (Note 2)

Note 1: CDH and CRS should not be set. The TSR however, could also

contain 01H, 03H, 07H and a variety of other values depending on whether collisions were encountered or the packet was deferred.

Note 2: Will contain 08H if packet is not transmittable.

Note 3: During external loopback the SNIC is now exposed to network traf-

fic, it is therefore possible for the contents of both the Receive portion of the FIFO and the RSR to be corrupted by any other packet on the network. Thus in a live network the contents of the FIFO and RSR should not be depended on. The SNIC will still abide by the standard CSMA/CD protocol in external loopback mode. (i.e., The network will not be disturbed by the loopback packet.)

Note 4: All values are hex.

CRC AND ADDRESS RECOGNITION

The next three tests exercise the address recognition logic and CRC. These tests should be performed using internal loopback only so that the SNIC is isolated from interference from the network. These tests also require the capability to generate CRC in software.

The address recognition logic cannot be directly tested. The CRC and FAE bits in the RSR are only set if the address in the packet matches the address filters. If errors are expected to be set and they are not set, the packet has been rejected on the basis of an address mismatch. The following sequence of packets will test the address recognition logic. The DCR should be set to 40H, the TCR should be set to 03H with a software generated CRC.

Packet Contents Results

Test Address CRC RSR

Test A Matching Good 01 (Note 1) Test B Matching Bad 02 (Note 2) Test C Non-Matching Bad 01

Note 1: Status will read 21H if multicast address used.

Note 2: Status will read 22H if multicast address used.

Note 3: In test A, the RSR is set up. In test B the address is found to match

since the CRC is flagged as bad. Test C proves that the address recognition logic can distinguish a bad address and does not notify the RSR of the bad CRC. The receiving CRC is proven to work in test A and test B.

Note 4: All values are hex.

NETWORK MANAGEMENT FUNCTIONS

Network management capabilities are required for maintenance and planning of a local area network. The SNIC supports the minimum requirement for network management in hardware, the remaining requirements can be met with software counts. There are three events that software alone can not track during reception of packets: CRC errors, Frame Alignment errors, and missed packets.

Page 36

12.0 Loopback Diagnostics (Continued)

Since errored packets can be rejected, the status associated with these packets is lost unless the CPU can access the Receive Status Register before the next packer arrives. In situations where another packet arrives very quickly, the CPU may have no opportunity to do this. The SNIC counts the number of packets with CRC errors and Frame Alignment errors. 8-Bit counters have been selected to reduce overhead. The counters will generate interrupts whenever their MSBs are set so that a software routine can accumulate the network statistics and reset the counter before overflow occurs. The counters are sticky so that when they reach a count of 192 (C0H) counting is halted. An additional counter is provided to count the number of packets the SNIC misses due to buffer overflow or being offline.

The structure of the counters is shown below:

TL/F/10469– 19

Additional information required for network management is available in the Receive and Transmit Status Registers. Transmit status is available after each transmission for information regarding events during transmission.

Typically, the following statistics might be gathered in software:

Traffic: Frames Sent OK

Frames Received OK Multicast Frames Received Packets Lost Due to Lack of Resources Retries/Packet

Errors: CRC Errors

Alignment Errors Excessive Collisions Packet with Length Errors Heartbeat Failure

Page 37

13.0 Bus Arbitration and Timing

The SNIC operates in three possible modes:

BUS MASTER (WHILE PERFORMING DMA)

BUS SLAVE (WHILE BEING ACCESSED BY CPU)

IDLE

Upon power-up the SNIC is in an indeterminate state. After receiving a hardware reset the SNIC is a bus slave in the Reset State, the receiver and transmitter are both disabled in this state. The reset state can be re-entered under three conditions, soft reset (Stop Command), hard reset (RESET input) or an error that shuts down the receiver of transmitter (FIFO underflow or overflow). After initialization of registers, the SNIC is issued a Start command and the SNIC enters Idle state. Until the DMA is required the SNIC remains in idle state. The idle state is exited by a request from the FIFO on the case of receiver or transmit, or from the Remote DMA in the case of Remote DMA operation. After acquiring

TL/F/10469– 20

the bus in a BREQ/BACK handshake the Remote or Local DMA transfer is completed and the SNIC re-enters the idle state.

DMA TRANSFERS TIMING

The DMA can be programmed for the following types of transfers:

16-Bit Address, 8-bit Data Transfer 16-Bit Address, 16-bit Data Transfer 32-Bit Address, 8-bit Data Transfer 32-Bit Address, 16-bit Data Transfer

All DMA transfers use BSCK for timing. 16-Bit Address modes require 4 BSCK cycles as shown below:

16-Bit Address, 8-Bit Data

TL/F/10469– 21

Page 38

13.0 Bus Arbitration and Timing (Continued)

16-Bit Address, 16-Bit Data

32-Bit Address, 8-Bit Data

TL/F/10469– 22

32-Bit Address, 16-Bit Data

Note: In 32-bit address mode, ADS1 is at TRI-STATE after the first T1 –T4 states: thus, a 4.7k pull-down resistor is required for 32-bit address.

TL/F/10469– 23

TL/F/10469– 24

Page 39

13.0 Bus Arbitration and Timing (Continued)

When in 32-bit mode four additional BSCK cycles are required per burst. The first bus cycle (T1 is used to output the upper 16-bit addresses. This 16-bit address is programmed in RSAR0 and RSAR1 and points to a 64k page of system memory. All transmitted or received packets are constrained to reside within this 64k page.

–T4Ê) of each burst

FIFO BURST CONTROL

All Local DMA transfers are burst transfers, once the DMA requests the bus and the bus is acknowledged, the DMA will transfer an exact burst of bytes programmed in the Data Configuration Register (DCR) then relinquish the bus. If there are remaining bytes in the FIFO the next burst will not be initiated until the FIFO threshold is exceeded. If BACK is removed during the transfer, the burst transfer will be aborted. (DROPPING BACK DURING A DMA CYCLE IS NOT

RECOMMENDED.)

where Ne1, 2, 4, or 6 Words or Ne2, 4, 8, or 12 Bytes when in byte mode.

INTERLEAVED LOCAL OPERATION

If a remote DMA transfer is initiated or in progress when a packet is being received or transmitted, the Remote DMA transfer will be interrupted for higher priority Local DMA

Note that if the FIFO requires service while a remote DMA is in progress, BREQ is not dropped and the Local DMA burst is appended to the Remote Transfer. When switching from a local transfer to a remote transfer, however, BREQ is dropped and raised again. This allows the CPU or other devices to fairly contend for the bus.

FIFO AND BUS OPERATIONS

Overview

To accommodate the different rates at which data comes from (or goes to) the network and goes to (or comes from) the system memory, the SNIC contains a 16-byte FIFO for buffering data between the bus and the media. The FIFO threshold is programmable, allowing filling (or emptying) the FIFO at different rates. When the FIFO has filled to its programmed threshold, the local DMA channel transfers these bytes (or words) into local memory. It is crucial that the local DMA is given access to the bus within a minimum bus latency time; otherwise a FIFO underrun (or overrun) occurs.

To understand FIFO underruns or overruns, there are two causes which produce this conditionÐ

TL/F/10469– 25

transfers. When the Local DMA transfer is completed the Remote DMA will rearbitrate for the bus and continue its transfers. This is illustrated below:

TL/F/10469– 26

1. the bus latency is so long that the FIFO has filled (or emptied) from the network before the local DMA has serviced the FIFO.

2. the bus latency or bus data rate has slowed the throughput of the local DMA to a point where it is slower than the network data rate (10 Mb/s). This second condition is also dependent upon DMA clock and word width (byte wide or word wide).

The worst case condition ultimately limits the overall bus latency which the SNIC can tolerate.

FIFO Underrun and Transmit Enable

During transmission, if a FIFO underrun occurs, the Transmit enable (TXE) output may remain high (active). Generally, this will cause a very large packet to be transmitted onto the network. The jabber feature of the transceiver will terminate the transmission, and reset TXE.

To prevent this problem, a properly designed system will not allow FIFO underruns by giving the SNIC a bus acknowledge within time shown in the maximum bus latency curves shown and described later.

Page 40

13.0 Bus Arbitration and Timing (Continued)

FIFO AT THE BEGINNING OF RECEIVE

At the beginning of reception, the SNIC stores entire Address field of each incoming packet in the FIFO to determine whether the packet matches its Physical Address Register or maps to one of its Multicast Registers. This causes the FIFO to accumulate 8 bytes. Furthermore, there are some synchronization delays in the DMA PLA. Thus, the actual time that BREQ is asserted from the time the Start of Frame Delimiter (SFD) is detected is 7.8 ms. This operation affects the bus latencies at 2 byte and 4 byte thresholds during the first receive BREQ since the FIFO must be filled to 8 bytes (or 4 words) before issuing a BREQ.

FIFO Operation at the End of Receive

When Carrier Sense goes low, the SNIC enters its end of packet processing sequence, emptying its FIFO and writing the status information at the beginning of the packet,

. The SNIC holds onto the bus for the entire sequence. The longest time BREQ may be extended occurs when a packet ends just as the SNIC performs its last FIFO burst. The SNIC, in this case, performs a programmed burst transfer followed by flushing the remaining bytes in the FIFO, and completes by writing the header information to memory. The following steps occur during this sequence.

1. SNIC issues BREQ because the FIFO threshold has been

reached

2. During the burst, packet ends, resulting in BREQ extend-

ed.

3. SNIC flushes remaining bytes from FIFO

4. SNIC performs internal processing to prepare for writing

the header.

5. SNIC writes 4-byte (2-word) header

6. SNIC deasserts BREQ

End of Packet Processing

Figure

End of Packet Processing Times for Various FIFO

Thresholds, Bus Clocks and Transfer Modes

Mode Threshold Bus Clock EOPP

Byte 2 bytes 7.0 ms

4 bytes 10 MHz 8.6 ms 8 bytes 11.0 ms

Byte 2 bytes 3.6 ms

4 bytes 20 MHz 4.2 ms 8 bytes 5.0 ms

Word 2 bytes 5.4 ms

4 bytes 10 MHz 6.2 ms 8 bytes 7.4 ms

Word 2 bytes 3.0 ms

4 bytes 20 MHz 3.2 ms 8 bytes 3.6 ms

Maximum Bus Latency for Byte Mode

TL/F/10469– 53

End of Packet Processing (EOPP) times for 10 MHz and 20 MHz have been tabulated below.

Maximum Bus Latency for Word Mode

TL/F/10469– 54

TL/F/10469– 55

Page 41

13.0 Bus Arbitration and Timing (Continued)

Threshold Detection (Bus Latency)

To assure that no overwriting of data in the FIFO occurs, the FIFO logic flags a FIFO overrun as the 13th byte is written into the FIFO, effectively shortening the FIFO to 13 bytes. The FIFO logic also operates differently in Byte Mode and in Word Mode. In Byte Mode, a threshold is indicated when

the n

1 byte has entered the FIFO; thus, with an 8 byte threshold, the SNIC issues Bus Request (BREQ) when the 9th byte has entered the FIFO. For Word Mode, BREQ is not generated until the n Thus, with a 4 word threshold (equivalent to 8 byte thres-

2 bytes have entered the FIFO.

Transmit Prefetch Timing

hold), BREQ is issued when the 10th byte has entered the FIFO. The two graphs indicate the maximum allowable bus latency for Word or Byte transfer modes.

The FIFO at the Beginning of Transmit

TL/F/10469– 56

Page 42

13.0 Bus Arbitration and Timing (Continued)

REMOTE DMA-BIDIRECTIONAL PORT CONTROL

The Remote DMA transfers data between the local buffer memory and a bidirectional port (memory to I/O transfer). This transfer is arbited on a byte by byte basis versus the burst transfer used for Local DMA transfers. This bidirec-

Bus Handshake Signals for Remote DMA Transfers

REMOTE READ TIMING

1. The DMA reads byte/word from local buffer memory and writes byte/word into latch, increments the DMA address and decrements the byte count (RBCR0, 1).

2. A Request Line (PRQ) is asserted to inform the system that a byte is available.

3. The system reads the port, the read strobe (RACK used as an acknowledge by the Remote DMA and it goes back to step 1.

)is

tional port is also read/written by the host. All transfers through this port are asynchronous. At any one time transfers are limited to one direction, either from the port to local buffer memory (Remote Write) or from local buffer memory to the port (Remote Read).

TL/F/10469– 27

Steps 1 – 3 are repeated until the remote DMA is complete.

Note that in order for the Remote DMA to transfer a byte from memory to the latch, it must arbitrate access to the local bus via a BREQ, BACK handshake. After each byte or word is transferred to the latch, BREQ is dropped. If a Local DMA is in progress, the Remote DMA is held off until the local DMA is complete.

TL/F/10469– 28

Page 43

13.0 Bus Arbitration and Timing (Continued)

REMOTE WRITE TIMING

A Remote Write operation transfers data from the I/O port to the local buffer RAM. The SNIC initiates a transfer by requesting a byte/word via the PRQ. The system transfers a byte-word to the latch via IOW by the SNIC and PRQ is removed. By removing the PRQ, the Remote DMA holds off further transfers into the latch until the current byte/word has been transferred from the latch, PRQ is reasserted and the next transfer can begin.

, this write strobe is detected

1. SNIC asserts PRQ. System writes byte/word into latch. SNIC removes PRQ.

2. Remote DMA reads contents of port and writes byte/ word to local buffer memory, increments address and decrements byte count (RBCR0, 1).

3. Go back to step 1.

Steps 1– 3 are repeated until the remote DMA is complete.

REMOTE DMA WRITE

Setting PRQ Using the Remote Read

Under certain conditions the SNIC’s bus state machine may issue MWR of a Remote Write Command. If this occurs this could cause data corruption, or cause the remote DMA count to be different from the main CPU count causing the system to ‘‘lock up.’’

To prevent this condition when implementing a Remote DMA Write, the Remote DMA Write command should first be preceded by a Remote DMA Read command to insure that the PRQ signal is asserted before the SNIC starts its port read cycle. The reason for this is that the state machine that asserts PRQ runs independently of the state machine that controls the DMA signals. The DMA machine assumes that PRQ is asserted, but actually may not be. To remedy this situation, a single Remote Read cycle should be inserted before the actual DMA Write Command is given. This will ensure that PRQ is asserted when the Remote DMA

and PRD before PRQ for the first DMA transfer

TL/F/10469– 29

Write is subsequently executed. This single Remote Read cycle is called a ‘‘dummy Remote Read.’’ In order for the dummy Remote Read cycle to operate correctly, the Start Address should be programmed to a known, safe location in the buffer memory space, and the Remote Byte Count should be programmed to a value greater than 1. This will ensure that the master read cycle is performed safely, eliminating the possibility of data corruption.

Remote Write with High Speed Buses

When implementing the Remote DMA Write solution with high speed buses and CPU’s, timing problems may cause the system to hang. Therefore additional considerations are required.

The problem occurs when the system can execute the dummy Remote Read and then start the Remote Write before the SNIC has had a chance to execute the Remote Read. If this happens the PRQ signal will not get set, and the Remote Byte Count and Remote Start Address for the Remote

Page 44

13.0 Bus Arbitration and Timing (Continued)

Note: The dashed lines indicate incorrect timing as described in the text.

FIGURE 9. Timing Diagram for Dummy Remote Read

Write operation could be corrupted. This is shown by the hatched waveforms in the timing diagram of

Figure 9

. The execution of the Remote Read can be delayed by the local DMA operations (particularly during end-of-packet processing).

To ensure the dummy Remote Read does execute, a delay must be inserted between writing the Remote Read Command, and starting to write the Remote Write State Address. (This time is designated in

Figure 9

by the delay arrows.) The recommended method to avoid this problem is after the Remote Read command is given, to poll both bytes of the Current Remote DMA Address Registers. When the address has incremented PRQ has been set. Software should recognize this and then start the Remote Write.

An additional caution for high speed systems is that the polling must follow guidelines specified in Time Between Chip Select section. That is, there must be at least 4 bus clocks between chip selects (for example when BSCK

MHz, then this time should be 200 ns).

TL/F/10469– 57

The general flow for executing a Remote Write is:

1. Set Remote Byte Count to a value

1 and Remote Start Address to unused RAM (one location before the transmit start address is usually a safe location).

2. Issue the ‘‘dummy’’ Remote Read command.

3. Read the Current Remote DMA Address (CRDA) (both bytes).

4. Compare to previous CRDA value if different go to 6.

5. Delay and jump to 3.

6. Set up for the Remote Write command, by setting the Remote Byte Count and the Remote Start Address (note that if Remote Byte count in step 1 can be set to the transmit byte count plus one, and the Remote Start Address to one less, these will now be incremented to the correct values.)

7. Issue the Remote Write command.

Page 45

13.0 Bus Arbitration and Timing (Continued)

SLAVE MODE TIMING

When CS can then read or write any internal registers. All register access is byte wide. The timing for register access is shown below. The host CPU accesses internal registers with four address lines, RA0 –RA3, SRD

is low, the SNIC becomes a bus slave. The CPU

and SWR strobes.

Write to Register

Read from Register

ADS0 is used to latch the address when interfacing to a multiplexed, address data bus. Since the SNIC may be a local bus master when the host CPU attempts to read or write to the controller, an ACK

line is used to hold off the CPU until the SNIC leaves master mode. Some number of BSCK cycles is also required to allow the SNIC to synchronize to the read or write cycles.

TL/F/10469– 30

TIME BETWEEN CHIP SELECTS

The SNIC requires that successive chip selects be no closer than 4 bus clocks (BSCK) together. If the condition is violated, the SNIC may glitch ACK

. CPUs that operate from pipe-

lined instructions (i.e., 386) or have a cache (i.e., 486) can

Time between Chip Selects

TL/F/10469– 31

execute consecutive I/O cycles very quickly. The solution is to delay the execution of consecutive I/O cycles by either breaking the pipeline or forcing the CPU to access outside its cache.

TL/F/10469– 58

Page 46

14.0 Preliminary Electrical Characteristics

Absolute Maximum Ratings

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications.

Supply Voltage (V

DC Input Voltage (V

DC Output Voltage (V

)

OUT

)

Storage Temperature Range (T

STG

)

0.5V toa7.0V

0.5V to V

65§Ctoa150§C

0.5V

Power Dissipation (PD) 800 mW

Lead Temp. (TL) (Soldering, 10 sec.) 260§C

ESD Rating (R

ZAP

1.5k, C

Preliminary DC Specifications T

120 pF) 1.5 kV

ZAP

0§Cto70§C, V

Symbol Parameter Conditions Min Max Units

IH2

IL2

Note 1: These levels are tested dynamically using a limited amount of functional test patterns, please refer to AC test load.

Note 2: Limited functional test patterns are performed at these input levels. The majority of functional tests are performed at levels of 0V and 3V.

Note 3: This is measured with a 0.1 mF bypass capacitor between V

Note 4: The low drive CMOS compatible V

guaranteed by testing the high drive TTL compatible V

Note 5: RA0– RA3, PRD pins the input leakage specification is I

Minimum High Level Output Voltage I (Notes 1, 4) I

Minimum Low Level Output Voltage I (Notes 1, 4) I

Minimum High Level Input Voltage (Note 2) 2.0 V

Minimum High Level Input Voltage For RACK WACK (Note 2)

Minimum Low Level Input Voltage (Note 2) 0.8 V

Minimum Low Level Input Voltage For RACK, WACK (Note 2)

Input Current V

Minimum TRI-STATE V Output Leakage Current (Note 5)

Average Supply Current X1e20 MHz Clock (Note 3) I

and GND.

and VOLlimits are not tested directly. Detailed device characterization validates that this specification can be

, WACK, BREQ and INT pins are used as outputs in test mode and as a result are tested as if they are TRI-STATE input/outputs. For these

and VOHspecification.

Note:

Absolute Maximum ratings are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the device should be operated at these limits.

Note:

All specifications in this datasheet are valid only if the mandatory isolation is employed and all differential signals are taken to exist at the AUI side of the isolation.

5Vg5%, unless otherwise specified.

20 mAV

2.0 mA 3.5 V

20 mA 0.1 V

2.0 mA 0.4 V

0.1 V

2.7 V

0.6 V

VCCor GND

OUT

0 mA 110 mA

OUT

VCCor GND

1.0

1.0 mA

10 mA

Page 47

14.0 Preliminary Electrical Characteristics (Continued)

Preliminary DC Specifications T

0§Cto70§C, Ve5Vg5%, unless otherwise specified.

Symbol Parameter Conditions Min Max Units

DIFFERENTIAL PINS (TXg,RXg, and CDg)

Diff. Output Voltage (TXg)78XTermination, and 270Xs from each to GNDg550g1200 mV

Diff. Output Voltage Imbalance (TXg) Same as Above Typical: 40 mV

Undershoot Voltage (TXg) Same as Above Typical: 80 mV

Diff. Squelch Threshold

and CDg)

(RX

Diff. Input Common Mode Voltage (RXgand CDg) (Note 1)

175b300 mV

0 5.25 V

OSCILLATOR PINS (X1 and GND/X2)

OSC

Note 1: This parameter is guaranteed by the isolation and is not tested.

X1 Input High Voltage X1 is Connected to an Oscillator

and GND/X2 is Grounded

2.0 V

X1 Input Low Voltage Same as Above 0.8 V

X1 Input Current GND/X2 is Grounded

VCCor GND

3mA

Page 48

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary

TL/F/10469– 32

Symbol Parameter Min Max Units

rss Register Select Setup to ADS0 Low 10 ns

rsh Register Select Hold from ADS0 Low 13 ns

aswi Address Strobe Width In 15 ns

ackdv Acknowledge Low to Data Valid 55 ns

rdz Read Strobe to Data TRI-STATE (Note 3) 15 70 ns

rackl Read Strobe to ACK Low (Notes 1, 2) n*bcyca30 ns

rackh Read Strobe to ACK High 30 ns

rsrsl Register Select to Slave Read Low,

Latched RS0–3

Note 1: ACK is not generated until CS and SRD are low and the SNIC has synchronized to the register access. The SNIC will insert an integral number of Bus Clock cycles until it is synchronized. In Dual Bus systems additional cycles will be used for a local or remote DMA to complete. Wait states must be issued to the CPU until

is asserted low.

ACK

Note 2: CS

may be asserted before or after SRD.IfCSis asserted after SRD, rackl is referenced from falling edge of CS.CScan be de-asserted concurrently with

or after SRD is de-asserted.

SRD

Note 3: These limits include the RC delay inherent in our test method. These signals typically turn off within 15 ns, enabling other devices to drive these lines with no contention.

10 ns

Page 49

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Symbol Parameter Min Max Units

rsrs Register Select to Read Setup

(Notes 1, 3)

rsrh Register Select Hold from Read 0 ns

ackdv ACK Low to Valid Data 55 ns

rdz Read Strobe to Data TRI-STATE (Note 2) 15 70 ns

rackl Read Strobe to ACK Low (Note 3) n*bcyca30 ns

rackh Read Strobe to ACK High 30 ns

Note 1: rsrs includes flow-through time of latch.

Note 2: These limits include the RC delay inherent in our test method. These signals typically turn off within 15 ns enabling other devices to drive these lines with

no contention.

Note 3: CS

may be asserted before of after RA0 –3, and SRD, since address decode begins when ACK is asserted. If CS is asserted after RA0– 3, and SRD, rackl

is referenced from falling edge of CS

TL/F/10469– 33

10 ns

Page 50

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

TL/F/10469– 34

Symbol Parameter Min Max Units

rss Register Select Setup to ADS0 Low 10 ns

rsh Register Select Hold from ADS0 Low 17 ns

aswi Address Strobe Width In 15 ns

rwds Register Write Data Setup 20 ns

rwdh Register Write Data Hold 21 ns

ww Write Strobe Width from ACK 50 ns

wackh Write Strobe High to ACK High 30 ns

wackl Write Low to ACK Low (Notes 1, 2) n*bcyca30 ns

rswsl Register Select to Write Strobe Low 10 ns

Note 1: ACK is not generated until CS and SWR are low and the SNIC has synchronized to the register access. In Dual Bus Systems additional cycles will be used for a local DMA or Remote DMA to complete.

Note 2: CS

may be asserted before or after SWR.IfCSis asserted after SWR, wackl is referenced from falling edge of CS.

Page 51

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Symbol Parameter Min Max Units

rsws Register Select to Write Setup (Note 1) 15 ns

rswh Register Select Hold from Write 0 ns

rwds Register Write Data Setup 20 ns

rwdh Register Write Data Hold 21 ns

wackl Write Low to ACK Low (Note 2) n*bcyca30 ns

wackh Write High to ACK High 30 ns

ww Write Width from ACK 50 ns

Note 1: Assumes ADS0 is high when RA0 –3 changing.

Note 2: ACK

for a local DMA or remote DMA to complete.

is not generated until CS and SWR are low and the SNIC has synchronized to the register access. In Dual Bus systems additional cycles will be used

TL/F/10469– 35

Page 52

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

DMA Control, Bus Arbitration

TL/F/10469– 36

Symbol Parameter Min Max Units

brqhl Bus Clock to Bus Request High for Local DMA 50 ns

brqhr Bus Clock to Bus Request High for Remote DMA 45 ns

brql Bus Request Low from Bus Clock 60 ns

backs Acknowledge Setup to Bus Clock (Note 1) 2 ns

bccte Bus Clock to Control Enable 60 ns

bcctr Bus Clock to Control Release (Notes 2, 3) 70 ns

Note 1: BACK must be setup before T1 after BREQ is asserted. Missed setup will slip the beginning of the DMA by four bus clocks. The Bus Latency will influence the allowable FIFO threshold and transfer mode (empty/fill vs exact burst transfer).

Note 2: During remote DMA transfers only, a single bus transfer is performed. During local DMA operations burst mode transfers are performed.

Note 3: These limits include the RC delay inherent in our test method. These signals typically turn off within 15 ns enabling other devices to drive these lines with

no contention.

Page 53

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

DMA Address Generation

TL/F/10469– 37

Symbol Parameter Min Max Units

bcyc Bus Clock Cycle Time (Note 2) 50 125 ns

bch Bus Clock High Time 20 ns

bcl Bus Clock Low Time 20 ns

bcash Bus Clock to Address Strobe High 34 ns

bcasl Bus Clock to Address Strobe Low 44 ns

aswo Address Strobe Width Out bch ns

bcadv Bus Clock to Address Valid 45 ns

bcadz Bus Clock to Address TRI-STATE (Note 3) 15 55 ns

ads Address Setup to ADS0/1 Low bchb15 ns

adh Address Hold from ADS0/1 Low bclb5ns

Note 1: Cycles T1Ê,T2Ê,T3Êand T4Êare only issued for the first transfer in a burst when 32-bit mode has been selected.

Note 2: The rate of bus clock must be high enough to support transfers to/from the FIFO at a rate greater than the serial network transfers from/to the FIFO.

Note 3: These limits include the RC delay inherent in our test method. These signals typically turn off within 15 ns, enabling other devices to drive these lines with

no contention.

Page 54

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

DMA Memory Read

TL/F/10469– 38

Symbol Parameter Min Max Units

bcrl Bus Clock to Read Strobe Low 43 ns

bcrh Bus Clock to Read Strobe High 40 ns

ds Data Setup to Read Strobe High 22 ns

dh Data Hold from Read Strobe High 0 ns

drw DMA Read Strobe Width Out 2*bcycb15 ns

raz Memory Read High to Address TRI-STATE

(Notes 1, 2)

asds Address Strobe to Data Strobe bcla10 ns

dsada Data Strobe to Address Active bcycb10 ns

avrh Address Valid to Read Strobe High 3*bcycb18 ns

Note 1: During a burst A8 –A15 are not TRI-STATE if byte wide transfers are selected. On the last transfer A8– A15 are TRI-STATE as shown above.

Note 2: These limits include the RC delay inherent in our test method. These signals typically turn off within bch

lines with no contention.

15 ns, enabling other devices to drive these

bch

40 ns

Page 55

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

DMA Memory Write

TL/F/10469– 39

Symbol Parameter Min Max Units

bcwl Bus Clock to Write Strobe Low 40 ns

bcwh Bus Clock to Write Strobe High 40 ns

wds Data Setup to WR High 2*bcycb30 ns

wdh Data Hold from WR Low bcha7ns

waz Write Strobe to Address TRI-STATE (Notes 1, 2) bcha40 ns

asds Address Strobe to Data Strobe bcla10 ns

aswd Address Strobe to Write Data Valid bcla30 ns

Note 1: When using byte mode transfers A8 –A15 are only TRI-STATE on the last transfer, waz timing is only valid for last transfer in a burst.

Note 2: These limits include the RC delay inherent in our test method. These signals typically turn off within bch

lines with no contention.

15 ns, enabling other devices to drive these

Page 56

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Wait State Insertion

TL/F/10469– 40

Symbol Parameter Min Max Units

ews External Wait Setup to T3 0Clock (Note 1) 10 ns

ewr External Wait Release Time (Note 1) 15 ns

Note 1: The addition of wait states affects the count of deserialized bytes and is limited to a number of bus clock cycles depending on the bus clock and network rates. The allowable wait states are found in the table below. (Assumes 10 Mbit/sec data rate.)

of Wait States

BSCK (MHz)

80 1

10 0 1

12 1 2

14 1 2

16 1 3

18 2 3

20 2 4

Table assumes 10 MHz network clock.

Max

Byte Transfer Word Transfer

The number of allowable wait states in byte mode can be calculated using:

8 tnw

(byte mode)

tnw

tbsck

The number of allowable wait states in word mode can be calculated using:

(word mode)

4.5 tbsck

Number of Wait States

Network Clock Period

BSCK Period

5 tnw

2 tbsck

Page 57

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Remote DMA (Read, Send Command)

Symbol Parameter Min Max Units

bpwrl Bus Clock to Port Write Low 43 ns

bpwrh Bus Clock to Port Write High 40 ns

prqh Port Write High to Port Request High (Note 1) 30 ns

prql Port Request Low from Read Acknowledge High 60 ns

rakw Remote Acknowledge Read Strobe Pulse Width 20 ns

Note 1: Start of next transfer is dependent on where RACK is generted relative to BSCK and whether a local DMA is pending.

TL/F/10469– 41

Page 58

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Remote DMA (Read, Send Command) Recovery Time

Symbol Parameter Min Max Units

bpwrl Bus Clock to Port Write Low 43 ns

bpwrh Bus Clock to Port Write High 40 ns

prqh Port Write High to Port Request High (Note 1) 30 ns

prql Port Request Low from Read Acknowledge High 60 ns

rakw Remote Acknowledge Read Strobe Pulse Width 20 ns

rhpwh Read Acknowledge High to Next Port Write Cycle

(Notes 2, 3, 4)

Note 1: Start of next transfer is dependent on where RACK is generated relative to BSCK and whether a local DMA is pending.

Note 2: This is not a measured value but guaranteed by design.

Note 3: RACK

Note 4: Assumes no local DMA interleave, no CS

must be high for a minimum of 7 BSCK.

, and immediate BACK.

11 BSCK

TL/F/10469– 42

Page 59

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Remote DMA (Write Cycle)

TL/F/10469– 43

Symbol Parameter Min Max Units

bprqh Bus Clock to Port Request High (Note 1) 42 ns

wprql WACK to Port Request Low 52 ns

wackw WACK Pulse Width 25 ns

bprdl Bus Clock to Port Read Low (Note 2) 55 ns

bprdh Bus Clock to Port Read High 40 ns

Note 1: The first port request is issued in response to the remote write command. It is subsequently issued on T1 clock cycles following completion of remote DMA cycles.

Note 2: The start of the remote DMA write following WACK

is dependent on where WACK is issued relative to BSCK and whether a local DMA is pending.

Page 60

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Remote DMA (Write Cycle) Recovery Time

TL/F/10469– 44

Symbol Parameter Min Max Units

bprqh Bus Clock to Port Request High (Note 1) 42 ns

wprql WACK to Port Request Low 50 ns

wackw WACK Pulse Width 25 ns

bprdl Bus Clock to Port Read Low (Note 2) 55 ns

bprdh Bus Clock to Port Read High 40 ns

wprq Remote Write Port Request to Port

Request Time (Notes 3, 4, 5)

Note 1: The first port request is issued in response to the remote write command. It is subsequently issued on T1 clock cycles following completion of remote DMA cycles.

Note 2: The start of the remote DMA write following WACK

Note 3: Assuming wackw

Note 4: WACK

Note 5: This is not a measured value but guaranteed by design.

must be high for a minimum of 7 BSCK.

1 BSCK, and no local DMA interleave, no CS, immediate BACK, and WACK goes high before T4.

is dependent on where WACK is issued relative to BSCK and whether a local DMA is pending.

12 BSCK

Page 61

15.0 Switching Characteristics AC Specs DP83901A Note: All Timing is Preliminary (Continued)

Transmit Timing (End of Packet)

TL/F/10469– 47

TRANSMIT SPECIFICATIONS (End of Packet)

Symbol Parameter Min Max Units

TOH

TOI

Transmit Output High before Idle (Half Step) 200 ns

Transmit Output Idle Time tog40 mV(Half Step) 8000 ns

Reset Timing

TL/F/10469– 45

Symbol Parameter Min Max Units

rstw Reset Pulse Width (Note 1) 8 BSCK Cycles or TXC Cycles (Note 2)

Note 1: The RESET pulse requires the BSCK and TXC be stable. On power up, RESET should not be raised until BSCK and TXC have become stable. Several registers are affected by RESET

Note 2: The slower of BSCK or TXC clocks will determine the minimum time for the RESET

TXC then RESETe8cBSCK

If BSCK

BSCK then RESETe8cTXC

If TXC

. Consult the register descriptions for details.

signal to be low. TXC is X1 divided by 2.

16.0 AC Timing Test Conditions

All specifications are valid only if the mandatory isolation is employed and all differential signals are taken to be at the AUI side of the pulse transformer.

Input Pulse Levels (TTL/CMOS) GND to 3.0V

Input Rise and Fall Times (TTL/CMOS) 5 ns

Input and Output Reference Levles (TTL/CMOS) 1.3V

Input Pulse Levels (Diff.)

Input and Output 50% Point of

Reference Levels (Diff.) the Differential

TRI-STATE Reference Levels Float (DV)

Output Load (See Figure Below)

350 mV tob1315 mV

0.5V

Note 1: 50 pF, includes scope and jig capacitance

Note 2: S1

Open for timing tests for push pull outputs.

VCCfor VOLtest.

GND for VOHtest.

VCCfor High Impedance to active low and

active low to High Impedance measurements.

GND for High Impedance to active high and

active high to High Impedance measurements.

TL/F/10469– 48

Page 62

Pin Capacitance T

25§C, fe1 MHz

Symbol Parameter Typ Units

OUT

Input Capacitance 7 pF

Output Capacitance 7 pF

DERATING FACTOR

Output timings are measured with a purely capacitive load for 50 pF. The following correction factor can be used for other loads: C

50 pFa0.3 ns/pF.

Physical Dimensions inches (millimeters)

AUI Transmit Load

Note: In the above diagram, the TXaand TXbsignals are taken from the

AUI side of the isolation (pulse transformer). The pulse transformer used for all testing is the Pulse Engineering PE64103.

TL/F/10469– 49

DP83901A SNIC Serial Network Interface Controller

Plastic Chip Carrier (V)

Order Number DP83901V

NS Package Number V68A

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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Datasheet DP83901AV Datasheet (NSC)

Specifications and Main Features

Frequently Asked Questions

User Manual