AMD Advanced Micro Devices AM79C100JC Datasheet

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FINAL

Am79C100

Twisted-Pair Ethernet Transceiver Plus (TPEX Plus)

DISTINCTIVE CHARACTERISTICS

CMOS device provides IEEE 802.3-compliant
operation and low operating current from a
single +5 V supply

Power Down mode for reduced power
consumption in battery-powered applications

Automatic twisted-pair link integrity
Pin-selectable twisted-pair receive polarity

detection and automatic inversion of the receive
signal. Polarity indication output pin can
directly drive an LED.

Pin-selectable twisted-pair link integrity test
capability conforming to the IEEE 802.3
standard. Link status pin can directly drive
an LED.

Transmit, receive, and collision status
indications available on separate, dedicated
pins

Outputs can directly drive LEDs with pulses
stretched to ensure LED visibility

Internal twisted-pair transmitter digital
predistortion circuit to reduce medium-induced
jitter

Pin-selectable SQE Test (heartbeat) enable
AUI loopback, Jabber Control, and SQE Test

functions comply with the 10BASE-T standard
User-selectable loopback operations
Pin-selectable twisted-pair receive threshold

programming for extended distance line lengths

GENERAL DESCRIPTION

The Am79C100 Twisted-Pair Ethernet Transceiver Plus
(TPEX Plus) is an integrated circuit that implements the
medium attachment unit (MAU) functions for the
twisted-pair medium, as specified by the supplement to
the IEEE 802.3 standard (Type 10BASE-T). This de­vice provides the necessary electrical and functional
interface between the IEEE 802.3 standard attachment
unit interface (AUI) and the twisted-pair cable.

A network based on the 10BASE-T standard can use
unshielded twisted-pair cables, providing an economi­cal solution to networking by allowing the use of existing
telephone wiring. The Am79C100 provides a minimal
component count and a cost-effective solution to the
design and implementation of 10BASE-T standard
networks.

TPEX Plus provides twisted-pair driver and receiver cir­cuits, including on-board transmit digital predistortion,
receiver squelch, and an AUI port with pin-selectable
SQE Test enable. The device provides a number of ad­ditional features, including Link Status indication with
automatic twisted-pair receive polarity detection/
correction and indication; pin-selectable receive
threshold programming for extended distance line
lengths; and Receive Carrier Sense, Transmit Active
and Collision Present indications. The device provides
separate twisted-pair Link Status, Polarity Status,
Receive, Transmit, and Collision outputs to drive LEDs
directly.

Publication# 16511 Rev: BAmendment/0
Issue Date: May 1994

1

AMD

BLOCK DIAGRAM

DO+

DO–

CI+
CI–

DI+
DI–

Attachment 

Unit Interface

SQE TEST

PRDN/RST

(AUI)

REXT

TEST1TEST2

Line Receiver

and Squelch

Circuit

Line Driver

Line Driver

XMT COL RCV LNKST

RXPOL

LED Driver Logic

Jabber

Control

Collision and 

Loopback

Control



Polarity 

Detection and

Auto Correction

Voltage

Controlled

Oscillator

Line Driver

and

Predistortion

Link Test

State Machine

Line Receiver

and

Smart Squelch

TXD+
TXD–

TXP+

TXP–

RXD+

RXD–

LRT

Twisted-Pair

Interface

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)

TM

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TM

(ILACCTM)

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(HIMIBTM)



Plug n’ Play support)

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Am79C987 Hardware Implemented Management Information Base

16511B-1

2 Am79C100

CONNECTION DIAGRAM

DI–

DI+

PLCC

CI–

CI+

TXD+

TXD–

TXP+

LOGIC SYMBOL

DV
DV

XMT

LNKST

COL

AV

DO+

SS

SS

SS

6
7
8
9
10

11

121314

DO–

234

1

RCV

REXT

PRDN/RST

DV

DD

2827

1615

RXPOL

AV

26

1817

RXD–

DD

255
24

23
22

21
20
19

RXD+

TXP–
DV

DD

TEST2

TEST1
SQE TEST

LRT

AV

DD

16511B-2

Attachment

Unit Interface

(AUI)

DO+
DO–

DI+
DI–

CI+
CI–

SQE

TEST
TEST1
TEST2
REXT
PRDN/RST

DV

Am79C100

SS

AV

SS

TXD+
TXP+

TXD–

TXP–

RXD+
RXD–

LRT

RXPOL

LNKST

XMT
RCV

COL

Twisted-Pair
Interface

16511B-3

Am79C100 3

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.

AM79C100 J C

DEVICE NUMBER/DESCRIPTION

Am79C100
Twisted-Pair Ethernet Transceiver Plus (TPEX Plus)

Valid Combinations

AM79C100 JC

OPTIONAL PROCESSING

Blank = Standard Processing

OPERATING CONDITIONS

C = Commercial (0°C to +70°C)

PACKAGE TYPE

J = 28-Pin Plastic Leaded Chip Carrier (PL 028)

SPEED

Not Applicable

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.

4 Am79C100

PIN DESCRIPTION
AV

DD

Analog Power

This pin supplies +5 V to analog portions of the TPEX
Plus circuitry.

AV

SS

Analog Ground

This pin is the ground reference for analog portions of
TPEX Plus circuitry.

CI+, CI–

Control In
Output

AUI port differential driver.

COL

Collision
Output, Open Drain

This pin is driven LOW while the TPEX Plus is simulta­neously receiving data on the AUI DO pins and the
twisted-pair RXD pins, indicating that a collision condi­tion exists. It is also driven if TPEX Plus enters the jab­ber condition due to excessive length of activity on the
DO pair. In this case TPEX Plus will wait for a period of
inactivity on DO for the “unjab” time of 250 to 750 ms,
before the 10 MHz pattern on the CI pair is removed
and COL
SQE Test activity on the AUI CI pair. In the LOW output
state, the pin is capable of sinking a maximum of 12 mA
and can be used to drive an LED. The COL output is
pulse stretched for 20 to 62 ms after the end of colli­sion, to ensure LED visibility.

returns inactive. COL will not be driven during

DI+, DI–

Data In
Output

AUI port differential driver.

DO+, DO–

Data Out
Input

AUI port differential receiver.

DV

DD

Digital Power

This pin supplies +5 V to digital portions of the TPEX
Plus circuitry, including all transmit drivers.

DV

SS

Digital Ground

Two pins provide the ground reference for digital por­tions of TPEX Plus circuitry, including all transmit
drivers and the status indication LED drivers.

LNKST

Link Status
Input/Output, Open Drain

When this pin is tied LOW, the internal Link Test Re­ceive function is disabled, and the Transmit and
Receive functions will remain active regardless of arriv­ing idle link pulses and data. TPEX Plus continues to
generate idle link pulses irrespective of the status of
this pin.

As an output, this pin is driven LOW if the link is identi­fied as functional. However, if the link is determined to
be nonfunctional due to missing idle link pulses or data
packets, then this pin is not driven (internally pulled
HIGH). In the LOW output state, the pin is capable of
sinking a maximum of 12 mA and can be used to drive
an LED.

In the absence of an external drive, the pin is internally
pulled HIGH when inactive.

LR

T

Low Receive Threshold
Input, Active LOW

When this pin is tied LOW, the internal twisted-pair re­ceive thresholds are reduced by 4.5 dB from their orig­inal values (approximately 3/5 of the normal 10BASE-T
value). With LR
threshold for the RXD ± circuit will be 300 mV to 520 mV
peak. With LRT in the LOW state, the unsquelch
threshold for the RXD ± circuit will be 180 mV to 312 mV
peak. In either case, the RXD ± circuit post unsquelch
threshold will be approximately one-half of the initial
unsquelch threshold.

T in the HIGH state, the unsquelch

PRDN/RST

Power Down/Reset
Input, Active LOW

Driving this input LOW resets the internal logic of TPEX
Plus and places the device in a special Power Down
mode. In the Power Down/Reset mode, all output driv­ers are placed in their inactive state.

REXT

External Resistor
Input

An external precision resistor is connected between
this pin and AV
ence for the internal voltage-controlled oscillator
(VCO).

in order to provide a current refer-

DD

RCV

Receive
Output, Open Drain

This pin is driven LOW while TPEX Plus is receiving
data on the twisted-pair RXD pins and is transferring
the received signal onto the AUI DI pair. The output is
LOW during collision simultaneously with the COL

pin.

Am79C100 5

In the LOW output state, the pin is capable of sinking a
maximum of 12 mA and can be used to drive an LED.
The RCV
after the end of reception, to ensure LED visibility.

output is pulse stretched for 20 ms to 62 ms

RXD+, RXD–

Receive Data
Input

10BASE-T port differential receiver.

RXPOL

Receive Polarity
Input/Output, Open Drain

The twisted-pair receiver is capable of detecting a re­ceive signal with reversed polarity (wiring error). The
RXPOL pin is normally in the LOW state, indicating cor­rect polarity of the received signal. If the receiver de­tects a received packet with reversed polarity, then this
pin is not driven (goes HIGH) and the polarity of subse­quent packets is inverted. In the LOW output state, this
pin can sink up to a maximum of 12 mA and is therefore
capable of driving an LED.

This feature can be disabled by strapping this pin LOW.
In this case, the Receive Polarity correction circuit is
disabled and the internal Receive Signal remains non­inverted, irrespective of the received signal.

In the absence of an external drive, the pin is internally
pulled HIGH when inactive.

SQE

TEST

Signal Quality Test (Heartbeat) Enable
Input, Active LOW

The SQE Test function is enabled by tying this input
LOW. When enabled, TPEX Plus will send a 10 MHz
burst (heartbeat) on the CI ± lines after DO ± has be­come inactive, indicating integrity of the collision detec­tion and AUI circuitry. SQE
repeater applications.

In the absence of an external drive, the pin is internally
pulled HIGH when inactive.

TEST should be disabled for

TEST1

Test
Input, Active HIGH

This pin should be tied LOW for normal operation.
TEST1 permits system-level diagnostics to be per­formed. If TEST1 is driven HIGH (while TEST2
tained HIGH), TPEX Plus will enter the Loopback Test
mode. The type of loopback is determined by the state
of the SQE TEST pin. If SQE TEST is in the LOW state

is main-

(Station MAU), TPEX Plus transfers data indepen­dently from DO to the TXD/TXP circuits and from RXD
to the DI circuit. If the SQE
(Repeater MAU), then data on the RXD circuit is trans­mitted back onto the TXD/TXP circuits and data on the
DO circuit is transmitted onto the DI pair.

During either test mode, the Collision Detection and
SQE Test functions are disabled, and CI ± will remain
idle. Link beat pulses will continue to be generated nor­mally in the absence of TXD/TXP output activity, and
the Link Test Receive State Machine will be forced into
the Link Pass state. The COL
whenever a link beat pulse or transmit data activity
commences, and remain low during the output activity.
The receive squelch will continue to operate on both
the RXD ± and DO ± input circuits.

In the absence of an external drive, the pin is internally
pulled LOW.

TEST is in the HIGH state

pin will be driven LOW

TEST2

Test
Input, Active LOW

This pin should be tied HIGH for normal operation.

is reserved for factory testing, and should be

TEST2
permanently tied HIGH.

In the absence of an external drive, the pin is internally
pulled HIGH.

TXD+, TXD–

Transmit Data
Output

10BASE-T port differential drivers.

TXP+, TXP–

Transmit Predistortion
Output

Transmit waveform differential driver for predistortion.

XMT

Transmit
Output, Open Drain

This pin is driven LOW while TPEX Plus is receiving
data on the AUI DO pair and is transmitting data on the
TXD/TXP pins. The output is LOW during collision si­multaneously with the COL
state, the pin is capable of sinking a maximum of 12 mA
and can be used to drive an LED. The XMT output is
pulse stretched for 20 to 62 ms after the end of trans­mission, to ensure LED visibility.

pin. In the LOW output

6 Am79C100

FUNCTIONAL DESCRIPTION

The Twisted-Pair Ethernet Transceiver Plus (TPEX
Plus) complies with the requirements specified by the
IEEE 802.3 standard for the attachment unit interface
(AUI) and the 10BASE-T standard for a twisted-pair
medium attachment unit (MAU). TPEX Plus also imple­ments a number of features in addition to the IEEE

802.3 standard. An outline of the functions of the
Am79C100 is given below.

Attachment Unit Interface (DO ± , DI ± , CI ± )

The AUI electrical and functional characteristics com­ply with those specified within the IEEE 802.3 docu­ments, Sections 7 and 14. The AUI pins can be wired
to an isolation transformer, for a remote MAU applica­tion, or directly to another device (e.g., Am7992B serial
interface adapter), in the case of a local DTE applica­tion. The end-of-packet SQE Test function (heartbeat)
can be disabled to allow the device to be employed in a
repeater application.

Twisted-Pair Transmit Function

Data transmission to the 10BASE-T medium occurs
when valid AUI signals appear on the DO ± differential
pair. This data stream is routed to the differential driver
circuitry in the TXD ± and TXP ± pins. The driver circuitry
provides the necessary electrical driving capability and
the predistortion control for transmitting signals over
maximum length twisted-pair cable, as specified by the
IEEE 802.3 10BASE-T standard. During transmission,
data is looped back to the DI ± differential circuit, indi­cating normal operation. The transmit function for data
output and loopback operations meets the propagation
delays and jitter specified by the standard. During nor­mal transmission, and providing that TPEX Plus is not
in a Link Fail or Jabber state, the XMT pin will be driven
LOW, and can be used to drive a status LED directly.

Twisted-Pair Receive Function

The receiver complies with the receiver specifications
of the IEEE 802.3 10BASE-T standard, including noise
immunity and received signal rejection criteria (“Smart
Squelch”). Signals meeting these criteria appearing at
the RXD ± differential input pair are routed to the DI ±
outputs. The receiver function meets the propagation
delays and jitter requirements specified by the stan­dard. The receiver squelch level drops to approximately
half its threshold value after unsquelch to allow recep­tion of minimum amplitude signals and to mitigate car­rier fade in the event of worst-case signal attenuation
and crosstalk noise conditions. During receive, the
RCV pin is driven LOW and can be used to drive a sta­tus LED directly.

Note that the 10BASE-T standard defines the receive
input amplitude at the external media-dependent inter­face (MDI). Filter and transformer loss are not speci­fied. The TPEX Plus receiver squelch levels are defined

to account for a 1 dB insertion loss at 10 MHz, which is
typical for the type of receive filters/transformers rec­ommended (see also Table 1).

Normal 10BASE-T-compatible receive thresholds are
employed when the LR
the LRT pin is externally pulled LOW, the Low Receive
Threshold option is invoked, and the sensitivity of the
TPEX Plus receiver is increased. This allows longer
line lengths to be employed, exceeding the 100 m tar­get distance of normal 10BASE-T (assuming typical 24
AWG cable). The additional cable distance contributes
directly to increased signal attenuation and reduced
signal amplitude at the TPEX Plus receiver. However,
from a system perspective, making the receiver more
sensitive means that it is also more susceptible to
extraneous noise, primarily caused by coupling from
co-resident services (crosstalk). For this reason, it is
recommended that when using the Low Receive
Threshold option, the service should be installed on
4-pair cable only. Multipair cables within the same outer
sheath have lower crosstalk attenuation, may allow
noise emitted from adjacent pairs to couple into the re­ceive pair, and be of sufficient amplitude to falsely un­squelch the TPEX Plus.

T pin is inactive (HIGH). When

Link Test Function

The Link Test function is implemented as specified by
the 10BASE-T standard. During periods of transmit
pair inactivity, “link beat” pulses will be sent periodically
over the twisted-pair medium to allow constant monitor­ing of medium integrity.

When the Link Test function is enabled, the absence of
link beat pulses and receive data on the RXD ± pair will
cause the TPEX Plus to go into a Link Fail state. In the
Link Fail state, data transmission, data reception, data
loopback, and collision detection functions are disabled
and remain disabled until valid data or >5 consecutive
link pulses appear on the RXD ± pair. During Link Fail,
the LNKST pin is internally pulled HIGH. When the link
is identified as functional, the LNKST pin is driven
LOW, and is capable of directly driving a “Link OK”
LED. In order to interoperate with systems that do not
implement Link Test, this function can be disabled by
grounding the LNKST pin. With Link Test disabled, the
data driver, receiver, and loopback functions, as well as
collision detection, remain enabled irrespective of the
presence or absence of data or link pulses on the
RXD ± pair.

Polarity Detection and Reversal

The TPEX Plus receive function includes the ability to
invert the polarity of the signals appearing at the RXD ±
pair if the polarity of the received signal is reversed
(such as in the case of a wiring error). This feature al­lows data packets received from a reverse-wired RXD ±
input pair to be corrected in the TPEX Plus prior to
transfer to the DTE via the AUI interface (DI ± ). The

Am79C100 7

polarity detection function is activated following reset or
Link Fail, and will reverse the receive polarity based on
both the polarity of any previous link beat pulses and
the polarity of subsequent packets with a valid end
transmit delimiter (ETD).

When in the Link Fail state, TPEX Plus will recognize
link beat pulses of either positive or negative polarity.
Exit from the Link Fail state is caused by the reception
of 5 to 6 consecutive link beat pulses of identical polar­ity. On entry to the Link Pass state, the polarity of the
last 5 link beat pulses is used to determine the initial re­ceive polarity configuration and the receiver is reconfig­ured to subsequently recognize only link beat pulses of
the previously recognized polarity. This link pulse algo­rithm is employed only until SFD polarity determination
is made, as described later in this section.

Positive link beat pulses are defined as received signal
with a positive amplitude greater than 520 mV (LR
HIGH) with a pulse width of 60 ns to 200 ns. This posi­tive excursion may be followed by a negative excursion.
This definition is consistent with the expected received
signal at a correctly wired receiver, when a link beat
pulse that fits the template of Figure 14-12 in the
10BASE-T standard is generated at a transmitter and
passed through 100 m of twisted-pair cable.

Negative link beat pulses are defined as received sig­nals with a negative amplitude greater than 520 mV
(LRT = HIGH) with a pulse width of 60 ns to 200 ns.
This negative excursion may be followed by a positive
excursion. This definition is consistent with the ex­pected received signal at a reverse-wired receiver,
when a link beat pulse that fits the template of Figure
14-12 in the 10BASE-T standard is generated at a
transmitter and passed through 100 m of twisted-pair
cable.

The polarity detection/correction algorithm will remain
“armed” until two consecutive packets with valid ETD of
identical polarity are detected. When “armed,” the re­ceiver is capable of changing the initial or previous po­larity configuration based on the most recent ETD
polarity.

On receipt of the first packet with valid ETD following
reset or Link Fail, TPEX Plus will utilize the inferred po­larity information to configure its RXD ± input, regard­less of its previous state. On receipt of a second packet
with a valid ETD with correct polarity, the detection/cor­rection algorithm will “lock in” the received polarity. If
the second (or subsequent) packet is not detected as
confirming the previous polarity decision, the most re­cently detected ETD polarity will be used as the default.
Note that packets with invalid ETD have no effect on
updating the previous polarity decision. Once two con­secutive packets with valid ETD have been received,
TPEX Plus will disable the detection/correction

T =

algorithm until either a Link Fail condition occurs or
PRDN/RST

During polarity reversal, the RXPOL pin is internally
pulled HIGH. During normal polarity conditions, the
RXPOL pin is driven LOW, and is capable of directly
driving a “Polarity OK” LED using an integrated 12 mA
driver. If desired, the Polarity Reversal function can be
disabled by grounding the RXPOL pin.

is asserted.

Twisted-Pair Interface Status

Three outputs (XMT
the TPEX Plus is transmitting (AUI to twisted-pair), re­ceiving (twisted-pair to AUI), or in a collision state with
both functions active simultaneously.

The TPEX Plus will power up in the Link Fail state. The
normal algorithm will apply to allow it to enter the Link
Pass state. On power up, the XMT
drivers activate for 20 ms to 62 ms as a lamp test fea­ture, and will then go to their inactive state until TPEX
Plus enters the Link Pass state.

In the Link Pass state, transmit or receive activity that
passes the pulse-width/amplitude requirements of the
DO± or RXD± inputs will be indicated by the XMT or
RCV pin, respectively, going active. XMT, RCV, and
COL are all asserted during a collision.

In the Link Fail state, XMT , RCV, and COL are disabled.
In Jabber Detect mode, TPEX Plus will activate the

COL driver, disable the XMT driver (regardless of DO±
activity), and allow the RCV driver to indicate the cur­rent state of the RXD± pair. If there is no receive activity
on RXD±, only COL will be active during Jabber Detect.
If there is RXD± activity, both COL and RCV will be
active.

All three outputs are active LOW and incorporate 12
mA drive capability with 20 ms to 62 ms pulse stretch
circuitry, to extend the event to ensure LED visibility.

, RCV, and COL) indicate whether

, RCV, and COL LED

Collision Detect Function

Simultaneous Carrier Sense (presence of valid data
signals) by both the AUI DO± pins and the twisted-pair
RXD± pins constitutes a collision, thereby causing a
10 MHz signal to be asserted on the CI± output pair,
and the COL output to be activated. The CI± output
meets the drive requirements for the AUI interface. This
10 MHz signal will remain on the CI± pair until one of
the two colliding states changes from active to idle.
During the collision condition, data presented on the
DI± pair will be sourced from the RXD± input. At the
end of collision, the data presented on the DI± pair will
be sourced from the last remaining active input, either
RXD± or DO±. The CI± output pair stays HIGH for 2 bit
times at the end of a collision, decreasing to the idle
level within 80 bit times after the last transition. The
XMT, RCV, and COL pins are driven LOW during
collision.

8 Am79C100