AMD Advanced Micro Devices AM7996PCB, AM7996PC, AM7996JCTR, AM7996JC, AM7996DCB Datasheet

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FINAL

Am7996

IEEE 802.3/Ethernet/Cheapernet Transceiver

DISTINCTIVE CHARACTERISTICS

Compatible with Ethernet Version 2 and
IEEE 802.3 10BASE-5and10BASE-2
specifications

Pin-selectable SQE Test (heartbeat) option
Internal jabber controller prevents excessive

transmission time

GENERAL DESCRIPTION

The Am7996 IEEE 802.3/Ethernet/Cheapernet Trans­ceiver supports Ethernet Version 2, IEEE 802.3
10BASE-5 and IEEE 802.3 10BASE-2—Cheapernet)
transceiver applications. Transmit, receive, and colli­sion detect functions at the coaxial media interface to
the data terminal equipment (DTE) are all performed by
this single device.

In an IEEE 802.3 (10BASE-5)/Ethernet application, the
Am7996 interfaces the coaxial (0.4 ″ diameter) media to the
DTE through an isolating pulse transformer and the 78 Ω
attachment unit interface (AUI) cable. In IEEE 802.3
10BASE-2—Cheapernet applications, the Am7996 typi­cally resides inside the DTE with its signals to the DTE iso­lated and the coaxial (0.2 ″ diameter) media directly

Noise rejection filter ensures that only valid data
is transmitted onto the network

Collision detection on both transmit and receive
data

Collision detect threshold levels adjustable for
other networking applications

connected to the DTE. Transceiver power and ground in
both applications are isolated from that of the DTE.

The Am7996’s tap driver provides controlled skew and
current drive for data signaling onto the media. The jabber
controller prevents the node from transmitting exces­sively. While transmitting, collisions on the media are de­tected if one or more additional stations are transmitting.

The Am7996 features an optional SQE Test function
that provides a signal on the Cl pair at the end of every
transmission. The SQE Test indicates the operational
status of the Cl pair to the DTE. It can also serve as an
acknowledgment to the node that packet transmission
onto the coax was completed.

BLOCK DIAGRAM

DI+

DI–

CI+

CI–

AUI Interface

DO+
DO–

SQE TEST

Publication# 07506 Rev: EAmendment/0
Issue Date: May 1994

Line

Driver

Line

Driver

Control

Logic

Control

Logic

Input

Buffer

Carrier
Detect

Circuit

Receive

Data

Amplifier

Collision

Detect
Circuit

Jabber

Timer

SQE Test
Generator

Transmit

Squelch

Transmit

Data

Amplifier

Input

Buffer

Tap

Driver

RXT

Coaxial Media Interface

TXT

07506E-1

1

AMD

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Am79C961 PCnet-ISA

+

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CONNECTION DIAGRAMS

DIP PLCC

V

CI+
CI–
DI+

DI–

V

C

SQE^TEST

DO+
DO–

V

Notes:

Pin 1 is marked for orientation.
NC = No Connection

CC1

REF

1
2

3
4
5
6
7

8
9
10

EE

20
19
18
17
16
15
14
13
12
11

V

CC2

COLL OSC
V

COL

NC
RXT

NC
TAP SHIELD
V

TX–

TXT
V

TX+

07506E-2

DI+
DI–

VC

REF

SQE^TEST

DO+

CI+

CI–

3212019
4
5
6
7
8

91011

EE

V

DO–

CC1

V

1213

TX+

V

CC2

V

COLL OSC

18
17
16
15
14

TX–

V

TXT

V

COL

NC
RXT
NC
TAP SHIELD

07506E-3

2 Am7996

ORDERING INFORMATION
Standard Products

AMD standard products are available in several packages and operating ranges. The order number (valid combination) is formed
by a combination of the elements below.

AM7996 D C

DEVICE NUMBER/DESCRIPTION

Am7996
IEEE 802.3/Ethernet/CheapernetTransceiver

B

OPTIONAL PROCESSING

Blank=Standard Processing
B=Burn-In
TR=Tape and Reel Packaging

OPERATING CONDITIONS

C = Commercial (0°C to +70°C)

PACKAGE TYPE

P=20-Pin Plastic DIP (PD 020)
D=20-Pin Ceramic DIP (CD 020)
J=20-Pin Plastic Leaded Chip Carrier (PL 020)

SPEED

Not Applicable

AM7996

Valid Combinations

PC, PCB, DC, DCB,

JC, JCTR

Valid Combinations

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

Am7996 3

PIN DESCRIPTION
Attachment Unit Interface (AUI)
Dl+, Dl–

Receive Line Output (Differential Outputs)

This pair is intended to operate into terminated 78 Ω
transmission lines. Signals at RXT meeting bandwidth
requirements and carrier sense levels are outputted at
Dl ± . Signaling at Dl ± meets requirements of
IEEE 802.3, Rev. D.

Cl+, Cl–

Collision Line Output (Differential Outputs)

This pair is intended to operate into terminated 78 Ω
transmission lines. Signal Quality Error (SQE), de­tected at DO ± inputs (excessive transmissions) or RXT
input (during a collision), outputs the 10 MHz internal
oscillator signal to the AUI interface. For proper compo­nent values at COLL OSC, signaling at Cl ± meets re­quirements of IEEE 802.3, Rev. D.

DO+, DO–

Transmit Input (Differential Inputs)

A pair of internally biased line receivers consisting of a
squelch detect receiver with offset and noise filtering
and a data receiver with zero offset for data signal pro­cessing. Signals meeting squelch requirements are
waveshaped and output at TXT.

Coaxial Media Interface (TAP)
RXT

Media Signal Receiver Input (Input)

RXT connects to the media through a 4:1 attenuator of
100 k Ω total resistance (25 k Ω and 75 k Ω in series).
Return for the attenuator is V

. RXT is an analog

COL

input with internal AC coupling for Manchester data sig­nals and direct coupling for Carrier Detect and SQE av­erage level detection. Signals at RXT meeting carrier
squelch enable data to the Dl ± outputs. Data signals
are AC coupled to Dl ± with a 150 ns time constant,
high-pass filter. Signals meeting SQE levels enable
COLL OSC frequency to Cl ± outputs.

TXT

Tap Node Driver (Input/Output)

A controlled bandwidth current source and sense am­plifier. This l/O port is to be connected to the media
through an isolation network and a low-pass filter. Sig­nals meeting DO ± squelch and jabber timing require­ments are output at TXT as a controlled rise and fall
time current pulse. When operated into a double termi­nated 50 Ω transmission line, signaling meets
IEEE 802.3, Rev. D recommendations for amplitude,
pulse-width distortion, rise and fall times, and harmonic
content. The sense amplifier monitors TXT faults and
inhibits transmission.

Global Signals
VC

REF

Timing Reference Set (Input)

VC

is a compensated voltage reference input with

REF

respect to V
VC

and V

REF

. When a resistor is connected between

EE

, then internal transmit and receive

EE

squelch timing, SQE oscillator frequency, and receive
and SQE output drive levels are set. SQE frequency
set is also determined by components connected be­tween V

SQE

and COLL OSC.

CC1

TEST

Signal Quality Error Test Enable (Input)

The SQE Test function is enabled by connecting the

TEST pin to V

SQE

V

TX+

, V

TX–

and disabled by connecting to V

EE

CC

Tap Node Driver Current Set (Inputs)

A reference input for transmission level and external re­dundant jabber. Transmit level is set by an external re­sistor between V
R = 9.09 Ω ). V
V

+ 1 V. When the voltage at V

EE

than V

+ 2 V, TXT is disabled and an SQE message

EE

and V

TX+

may be operated between V

TX–

(for an 80 mA peak level,

TX–

goes more positive

TX–

EE

and

is output at the Cl pair.

TAP SHIELD

Low-Noise Media Cable Return (Input)

This input is the return for V

reference and the re-

COL

ceive signal from the media. External connection is to
a positive power supply.

V

COL

SQE Reference Voltage (Bias Supply)

SQE sense voltage and RXT input amplifier reference.
An internally set analog reference for SQE level and data
signal set at –1.600 V nominal with a source resistance
of 150 Ω nominal. This reference should be filtered with
respect to TAP SHIELD (see Applications section for ad­justing threshold levels for other applications).

COLL OSC

SQE Timing Set (Input)

Timing input for SQE oscillator. For a properly set input
at VC
10 MHz SQE oscillator frequency, R should be 1 k Ω and
C 47 pF, including interconnect and device capacitance.

V

Positive Logic Supply

V

SQE Timing Reference (Positive Supply Voltage)

Timing reference return for SQE oscillator and analog
signal ground.

V

Negative Logic Supply and IC Substrate

, SQE oscillator period is set at 2.1RC. For a

REF

CC1

CC2

EE

.

4 Am7996

FUNCTIONAL DESCRIPTION

The Am7996 IEEE 802.3/Ethernet/Cheapernet Trans­ceiver consists of four sections: 1) Transmit—receives
signals from DTE and sends it to the coaxial medium;

2) Receive—obtains data from media and sends it to
DTE; 3) Collision Detect—indicates to DTE any colli­sion on the media; and 4) Jabber—guards medium
from node transmissions that are excessive in length.

Transmit

The Am7996 receives differential signals from the DTE
(in the case of Am7990 family applications, from the
Am7992—serial interface adapter—SIA). For IEEE
(10BASE-5)/Ethernet applications, this signal is re­ceived through the AUI cable and isolation transformer.
In IEEE 802.3 10BASE-2—Cheapernet applications,
the AUI cable is optional.

Data is received through a noise rejection filter that re­jects signals with pulse widths less than 7 ns (negative
going), or with levels less than 175 mV peak. Only sig­nals greater than –275 mV peak from the DTE are en­abled. This minimizes false starts due to noise and
ensures that no valid packets are missed.

The Am7996’s tap driver provides the driving capability
to ensure adequate signal level at the end of the maxi­mum length network segment (500 meters) under the
worst-case number of connections (100 nodes). Re­quired rise and fall times of data transmitted on the net­work are maintained by the Am7996 Tap Driver. The tap
driver’s output is connected to the media through exter­nal isolating diodes. To safeguard network integrity, the
driver is disabled whenever power falls below the mini­mum operation voltage.

During transmission, the Am7996 Jabber Controller
monitors the duration that the transmit tap driver is ac­tive and disables the driver if the jabber time is ex­ceeded. This prevents network tie-up due to a
“babbling” transceiver. Once disabled, the driver is not
reset until 400 ms after the DO pair is idle and there is
no fault on TXT. During the disable time, an SQE signal
is sent on the Cl pair to the DTE.

When SQE
an SQE message at the end of every transmission. This
signal is a self-test indication to the DTE that the media
attachment unit (MAU) collision pair is operational.

TEST is tied to V

, the Am7996 generates

EE

Receive and Carrier Detect

Signal is acquired from the tap through a high­impedance (100 k Ω ) resistive divider. A high input­impedance (low capacitance, high bandwidth, low
noise) DC-coupled input amplifier in the Am7996 re­ceives the signal. The received signal passes through
a high-pass filter to minimize inter-symbol distortion,
and then through a data slicer. The Am7996 Carrier
Detect compares received signals to a reference.
Signals meeting carrier squelch requirements enable

data to the differential line driver within five bit times
from the start of the packet.

Received data is transmitted from the Dl pair through
an isolation transformer to the AUI cable (Ethernet/
lEEE 802.3—10BASE-5). In IEEE 802.3 10BASE-2—
Cheapernet, the AUI cable is optional. Following the
last transition of the packet, the Dl pair is held HIGH for
two bit times and then decreases to idle level within
twenty bit times.

Collision Detect

The Am7996 detects collisions on transmit if one or
more additional stations are transmitting on the network.

Received signals are compared against the collision
threshold reference. If the level is more negative than
the reference, an enable signal is generated to the Cl
pair. The collision threshold can be modified by
external components.

The collision oscillator is a 10 MHz oscillator that drives
the differential Cl pair to the DTE through an isolation
transformer.

This signal is gated to the Cl pair whenever there is a
collision, the SQE Test is in progress, or the jabber con­troller is activated. The oscillator is also utilized in
counting time for the jabber timer and SQE Test.

The Cl ± output meets the drive requirements for the
AUI interface. The output stays HIGH for two bit times
at the end of the packet, decreasing to the idle level
within twenty bit times.

Jabber Function

The Am7996 Jabber Timer monitors the activity on the
DO pair and senses TXT faults. It inhibits transmission
if the tap driver is active for longer than the jabber time
(26 ms). An SQE message (10 MHz collision signal), is
enabled on the Cl pair for the fault duration.

After the fault is removed, the jabber timer counts the
unjab time of 400 ms before it enables the driver.

If desired, a redundant jabber function can be imple­mented externally, and the output driver disabled by re­moving the driver supply at V
this condition and forces an SQE message on the Cl
pair during the disable time.

.The Am7996 senses

TX–

SQE Test

An SQE Test will occur at the end of every transmission
if the SQE
is a gated 10 MHz signal to the Cl pair. The SQE Test en­sures that the twisted-pair assigned for collision notifica­tion to the DTE is intact and operational. The SQE Test
starts eight bit times after the last transition of the trans­mitted signal and lasts for a duration of eight bit times.

The SQE Test can be disabled by connecting the
SQE

TEST pin is tied to V

TEST pin to V

CC

. The SQE Test signal

EE

.

Am7996 5

AMD

APPLICATIONS

The Am7996 is compatible with Ethernet Version 2 and
IEEE 802.3 10BASE5 and 10BASE2 applications. (See
Figure 1).

MAU

Ethernet

Local

CPU

AUI - Attachment Unit Interface
DTE - Data Terminal Equipment
MAU - Media Access Unit

Cheapernet

Local

CPU

Local

Memory

Local Bus

Local

Memory

Local Bus

Am7990

LANCE

Am7990

LANCE

Figure 1. Typical Ethernet Node

Table 1. Transmit Mode Collision Detect

Function Table

MAU

Mode of Operation < 2 = 2 > 2

Transmitting No Yes Yes

Not Transmitting No May Yes

Number of Transmitters

DTE

Am7992B

SIA

DTE

Am7992B

SIA

AUI

Cable

Am7996

Transceiver

Power

Supply

Am7996

Transceiver

Power

Supply

Table 3. Receive Mode Collision Detect

Function Table

MAU

Mode of Operation < 2 = 2 > 2

Transmitting No Yes Yes

Not Transmitting No Yes Yes

Number of Transmitters

Tap

Ethernet

Coax

RG58

BNC "T"

07506E-4

Table 2. IEEE 802.3 Recommended Transmit

Mode Collision Detect Thresholds

Threshold Voltage Level

IEEE 802.3

No Detect Must Detect

10BASE5, Ethernet –1.492 V –
10BASE2, Cheapernet –1.404 V –1.782 V

6 Am7996

Table 4. IEEE 802.3 Recommended Receive

Mode Collision Detect Thresholds

Threshold Voltage Level

IEEE 802.3

10BASE5, Ethernet –1.492 V –1.629 V
10BASE2, Cheapernet –1.404 V –1.581 V

No Detect Must Detect