AM79C873 Advanced Micro Devices, AM79C873 Datasheet - Page 16

• Manufacturer Part Number: AM79C873
• Description: NetPHY -1 10/100 Mbps Ethernet Physical Layer Single-Chip Transceiver with 100BASE-FX Support
• Manufacturer: Advanced Micro Devices

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:
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
16
Binary In
Binary In
MLT-3
Figure 4. MLT-3 Converter Block Diagram
D
CK
Q
Q
P R E L I M I N A R Y
Am79C873
Binary plus
Binary minus
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.
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
Signal Detect
Adaptive Equalization
MLT-3-to-Binary Decoder
Clock Recovery Module
NRZI -o-NRZ Decoder
Serial-to-Parallel Converter
Descrambler
Code Group Alignment
4B5B Decoder
Common
Driver
MLT-3
22164A-6