AM79C873 datasheet(16/44 Pages) AMD

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Am79C873

PRELIMINARY

MLT-3 Driver

The two binary data streams created at the MLT-3 con-

verter are fed to the twisted pair output driver which

converts these streams to current sources and alter-

nately drives either side of the transmit transformer pri-

mary winding resulting in a minimal current MLT-3

signal. Refer to Figure 4 for the block diagram of the

MLT-3 converter.

100BASE Receiver

The 100BASE receiver contains several function

blocks that convert the scrambled 125 Mbps serial data

to synchronous 4-bit nibble data that is then provided to

the MII.

The receive section contains the following functional

blocks:

s Signal Detect

s Adaptive Equalization

s MLT-3-to-Binary Decoder

s Clock Recovery Module

s NRZI -o-NRZ Decoder

s Serial-to-Parallel Converter

s Descrambler

s Code Group Alignment

s 4B5B Decoder

100BASE-TX Signal Detect

The signal detect function meets the speciﬁcations man-

dated by the ANSI XT12 TP-PMD 100BASE-TX stan-

dards for both voltage thresholds and timing parameters.

Figure 4.

MLT-3 Converter Block Diagram

100BASE-FX Signal Detect

The NetPHY-1 device accepts signal detect information

on the FXSD pin at PECL signal levels from the FX

Optical Module.

Adaptive Equalization

When transmitting data at high speeds over copper

twisted pair cable, attenuation based on frequency be-

comes a concern. In high speed twisted pair signaling,

the frequency content of the transmitted signal can

vary greatly during normal operation based on the ran-

domness of the scrambled data stream. This variation

in signal attenuation caused by frequency variations

must be compensated for to ensure the integrity of the

received data.

In order to ensure quality transmission when employing

MLT-3 encoding, the compensation must be able to

adapt to various cable lengths and cable types depend-

ing on the installed environment. The selection of long

cable lengths for a given implementation, requires sig-

niﬁcant compensation which will be over-kill in a situa-

tion that includes shorter, less attenuating cable

lengths. Conversely, the selection of short or intermedi-

ate cable lengths requiring less compensation will

Binary In

Binary minus

Binary plus

MLT-3

Binary In

Common

Driver

22164A-6

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