AM79C100JC datasheet(6/24 Pages) AMD

6 / 24 page

Am79C100

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 output is pulse stretched for 20 ms to 62 ms

after the end of reception, to ensure LED visibility.

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 re-

ceive signal with reversed polarity (wiring error). The

RXPOL pin is normally in the LOW state, indicating cor-

rect polarity of the received signal. If the receiver de-

tects a received packet with reversed polarity, then this

pin is not driven (goes HIGH) and the polarity of subse-

quent 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 non-

inverted, 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 be-

come inactive, indicating integrity of the collision detec-

tion and AUI circuitry. SQE TEST should be disabled for

repeater applications.

In the absence of an external drive, the pin is internally

pulled HIGH when inactive.

TEST1

Test

Input, Active HIGH

This pin should be tied LOW for normal operation.

TEST1 permits system-level diagnostics to be per-

formed. If TEST1 is driven HIGH (while TEST2 is main-

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

(Station MAU), TPEX Plus transfers data indepen-

dently from DO to the TXD/TXP circuits and from RXD

to the DI circuit. If the SQE TEST is in the HIGH state

(Repeater MAU), then data on the RXD circuit is trans-

mitted 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 nor-

mally 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 pin will be driven LOW

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.

TEST2

Test

Input, Active LOW

This pin should be tied HIGH for normal operation.

TEST2 is reserved for factory testing, and should be

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 si-

multaneously with the COL pin. 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 XMT output is

pulse stretched for 20 to 62 ms after the end of trans-

mission, to ensure LED visibility.

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