82503 Datasheet, PDF (12/45 Pages) Intel Corporation – DUAL SERIAL TRANSCEIVER (DST)

82503
Figure 6 Manchester Decoder and Clock Recovery
290421 – 5
3 3 2 AUI RECEIVE AND COLLISION BUFFERS
The AUI receive and collision inputs are driven
through isolation transformers to provide high volt-
age protection and DC common mode voltage rejec-
tion The incoming signals are converted to digital
levels and passed to the Manchester decoder and
collision detection circuitry
3 3 3 AUI RECEIVE AND COLLISION
SQUELCH CIRCUITS
Both the receive (RCV) and collision (CLSN) pairs
have the following squelch characteristics
 The squelch circuits are turned on at idle
 A pulse is rejected if the peak differential voltage
is more positive than ^b160 mV regardless of
pulse width
 A pulse is considered valid if its peak differential
voltage is more negative than ^b300 mV and its
width measured at ^b285 mV is greater than
25 ns
 The squelch circuits are disabled by the first valid
negative differential pulse on either the AUI re-
ceive (RCV) or the AUI collision (CLSN) pair
 If a positive differential pulse occurs on either the
AUI receive or collision pairs for greater than
160 ns End of Frame (EOF) is assumed and the
squelch circuitry is turned on
3 3 4 TPE RECEIVE BUFFER
The TPE receive pins (RD and RD) are connected to
the twisted pair medium through an analog front
end The analog front end contains the line coupling
devices and EMI filters necessary to conform to the
10BASE-T standards and local RF regulations The
input differential voltage range for the TPE receiver
is greater than 500 mV and less than 3 1V differen-
tial
3 3 5 TPE RECEIVE SQUELCH CIRCUITS
The TPE receive buffer distinguishes valid receive
differential data link test pulses and the idle condi-
tion according to the requirements of the 10BASE-T
standard Signals at the output of the EMI filter (thus
at the RD and RD pair) are rejected as follows
 All differential pulses of peak magnitude less than
300 mV are rejected
 All continuous sinusoids with a differential ampli-
tude less than 6 2 V_PP and a frequency less than
2 MHz are rejected
 All sine waves of single cycle duration starting
with phase 0 or 180 that have an amplitude less
than 6 2 V_PP and a frequency of 2 MHz to
16 MHz are rejected if the single cycle is pre-
ceeded and followed by 4 bit times of silence
(i e a signal less than 300 mV)
3 3 6 TPE Extended Squelch Mode
By placing the 82503 into TPE extended squelch
mode the 82503 can support cable lengths greater
than the 100m specified in the 10Base-T IEEE stan-
dard (802 3i-1990) The squelch thresholds for the
signals at the RD RD pair are typically reduced by
4 5 dB This allows Grade 5 twisted-pair cable to be
used to overcome attenuation and multipair cross-
talk for cable lengths up to 200 meters
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