82503 datasheet(13/45 Pages) INTEL

13 / 45 page

82503

TPE extended squelch mode is enabled by present-

ing a high-impedance (l100 KX) at the APOLXSQ

pin This can be done by floating the APOLXSQ pin

tying APOLXSQ low through a 100 KX resistor or

driving APOLXSQ with a three-state buffer When

driven high or low using a TTL driver or a low imped-

ance pull-up or pull-down (k2KX) extended

squelch is disabled and the driven level at the

APOLXSQ pin determines the state of the polarity-

correction function (APOLXSQ e 1 enables polari-

ty correction APOLXSQ e 0 disables polarity cor-

rection) The TPE extended squelch feature is trans-

parent to previous steppings of the 82503 Polarity

correction is always enabled when the TPE extend-

ed-squelch feature is enabled (APOLXSQ e Z)

The APOLXSQ pin senses a high-impedance state

by an active-polling circuit implemented at the pin

Two small polling devices attempt to pull the APOL

XSQ pin up to VCC and down to VSS If the pin is in a

high-impedance state the devices will be successful

in pulling the APOLXSQ pin high and low If the pin

is driven high or low the polling devices will not be

able to successfully pull the pin in the opposite di-

rection In this way an internal state machine can

correctly determine one of three states of the

APOLXSQ pin The pin is polled every 256 ms

34 Collision Detection

341 AUI COLLISION DETECTION

Collision detection in the AUI mode is performed by

the attached transceiver and signalled to the 82503

on the CLSN pair A 10 MHz a25% or b15%

square wave with transition times between 35 ns

and 70 ns indicates the collision The 82503 reports

this to the LAN controller on the CDT pin

342 TPE COLLISION DETECTION

Collision detection in the TPE mode is indicated by

simultaneous transmission and reception on the

twisted pair link segment The CDT signal is assert-

ed for the duration of both RTS and the presence of

received data CRS is asserted for the duration of

either RTS or the presence of received data During

a collision the source of RxD will be the received

data If the received data stream ends before the

transmit data stream

the RxD source will be

changed to transmit data stream until it ends

35 Link Integrity

The 82503 supports the link integrity function as de-

fined by 10BASE-T During long periods of idle on

the transmitter link test pulses will be transmitted on

to the twisted pair medium as an indication to the

remote MAU that the link is good These pulses will

be transmitted 8 ms to 24 ms after the end of the

last transmission or link test pulse

The link integrity function continuously monitors ac-

tivity on the receive circuit If neither valid data nor

link test pulses are received the link integrity proc-

essor declares the link bad and disables transmis-

sion and reception on the media loopback and the

SQE test function Transmission of link test pulses

and monitoring receive activity are not affected The

idle time required for the link integrity processor to

determine the link is bad is 50 ms to 150 ms

Once a frame or a sequence of 2 to 10 valid consec-

utive link test pulses are detected the Link Integrity

Processor declares the link is good and reconnects

the transmitter and receiver

The link integrity function can be disabled by driving

the LID pin high or by disabling automatic port selec-

tion (APORT e 0) and selecting the AUI port This

option is intended primarily for use with pre-

10BASE-T networks

36 Jabber Function

The 82503 contains a jabber timer to implement the

jabber function If a transmission continues beyond

the limits specified the jabber function inhibits fur-

ther transmission and asserts the collision indicator

CDT The limits for jabber transmission are 20 ms to

150 ms in TPE Mode and 8 ms to 16 ms in AUI

mode For both AUI and TPE mode the transmis-

sion inhibit period extends until the 82503 detects

sufficient idle time (between 250 ms and 750 ns) on

the RTS signal The jabber function can be disabled

by driving the JABD high

In TPE mode the link integrity function continues to

operate even if the jabber function is inhibiting trans-

mission Link test pulses continue to be sent and the

receive circuit continues to be monitored Additional-

ly the link integrity function reconnects to a restored

link without waiting for the transmit input to go idle

when the jabber function is inhibiting transmission

37 TPE Loopback

In TPE mode the 82503 implements the transmit to

receive loopback (DO to DI) mode specified in the

10BASE-T standard This mode loops back transmit-

ted data through the receive path

This function is required to maintain full compatibility

with coax MAUs where the data loopback is a natu-

ral result of the architecture

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