Datasheet

2.0 Functional Description (Continued)
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2.2 100BASE-TX TRANSMITTER
The 100BASE-TX transmitter consists of several functional
blocks which convert synchronous 4-bit nibble data, as pro-
vided by the MII, to a scrambled MLT-3 125 Mb/s serial data
stream. Because the 100BASE-TX TP-PMD is integrated,
the differential output pins, TPTD+/−, can be directly routed
to the AC coupling magnetics.
The block diagram in Figure 3 provides an overview of
each functional block within the 100BASE-TX transmit sec-
tion.
The Transmitter section consists of the following functional
blocks:
— Code-group Encoder and Injection block (bypass option)
— Scrambler block (bypass option)
— NRZ to NRZI encoder block
— Binary to MLT-3 converter / Common Driver
The bypass option for the functional blocks within the
100BASE-X transmitter provides flexibility for applications
such as 100 Mb/s repeaters where data conversion is not
always required. The DP83843 implements the 100BASE-
X transmit state machine diagram as specified in the IEEE
802.3u Standard, Clause 24.
– Code-group Encoding and Injection
Figure 1. 100BASE-TX Transmit Block Diagram
CODE-GROUP
ENCODER &
INJECTOR
SCRAMBLER
NRZ TO NRZI
ENCODER
PARALLEL
TO SERIAL
TPTD +/−
TX_CLK TXD[3:0] /
TX_ER
100BASE-X
LOOPBACK
MUX
MUX
MUX
BINARY
TO MLT-3 /
COMMON
DRIVER
25MHZ
BP_4B5B
BP_TX
BP_SCR