AM79C873 Advanced Micro Devices, AM79C873 Datasheet - Page 14

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

The block diagram in Figure 3 provides an overview of
the functional blocks contained in the transmit section.
The transmitter section contains the following func-
tional blocks:
The 4B5B encoder converts 4-bit (4B) nibble data gen-
erated by the MAC Reconciliation Layer into a 5-bit
(5B) code group for transmission (see Table 1). This
conversion is required for control and packet data to be
14
Signals
4B5B Encoder
MII
4B5B Encoder
Scrambler
Parallel-to-Serial Converter
NRZ-to-NRZI Converter
PECL Driver (For FX Operation)
NRZI to MLT-3 (For TX Operation)
MLT-3 Driver (For TX Operation)
Interface/
Control
MII
Encoder
4B/5B
Figure 3. 100BASE Transmitter Functional Block Diagram
Register
Scrambler
P R E L I M I N A R Y
Detection
Collision
25M OSCI
TX CGM
Parallel
to Serial
Am79C873
NRZI
NRZ
combined in code groups. The 4B5B encoder substi-
tutes the first 8 bits of the MAC preamble with a J/K
code-group pair (11000 10001) upon transmit.
The 4B5B encoder continues to replace subsequent
4B preamble and data nibbles with corresponding 5B
code-groups. At the end of the transmit packet, upon
the deassertion of the Transmit Enable signal from the
MAC Reconciliation layer, the 4B5B encoder injects the
T/R code-group pair (01101 00111) indicating end of
frame. After the T/R code-group pair, the 4B5B encoder
continuously injects IDLEs into the transmit data
stream until Transmit Enable is asserted and the next
transmit packet is detected.
The NetPHY-1 device includes a Bypass 4B5B conver-
sion option within the 100BASE-TX transmitter for sup-
port of applications like 100 Mbps repeaters which do
not require 4B5B conversion.
to
Carrier
Sense
NRZI to
MLT-3
Negotiation
LED1-4#
Driver
LED
Auto-
Rise/Fall
MLT-3
Driver
Time
CTL
10BASE-T
Module
RX
TX
PECL
Driver
22164A-5
100TXD
RXI
10TXD
FXTD