LU3X34FTR Datasheet, PDF (20/52 Pages) Agere Systems – Quad 3 V 10/100 Ethernet Transceiver TX/FX

LU3X34FTR
Quad 3 V 10/100 Ethernet Transceiver TX/FX
Preliminary Data Sheet
July 2000
Functional Description (continued)
100Base-X Transmitter
The 100Base-X transmitter consists of functional
blocks which convert synchronous 4-bit nibble data, as
provided by the internal MII, to a 125 Mbits/s serial
data stream. This data stream may be routed either to
the on-chip twisted-pair PMD for 100Base-TX signal-
ing, or to an external fiber-optic PMD for 100Base-FX
applications. The LU3X34FTR implements the
100Base-X transmit state machine as specified in the
IEEE 802.3u Standard, Clause 24 and comprises the
following functional blocks in its data path:
s Symbol encoder.
s Scrambler block.
s Parallel/serial converter and NRZ/NRZI encoder
block.
Symbol Encoder
The symbol encoder converts 4-bit (4B) nibble data
generated by the RMII-MII module into 5-bit (5B) sym-
bols for transmission. This conversion is required to
allow control symbols to be combined with data sym-
bols. Refer to Table 11 for 4B to 5B symbol mapping.
Following onset of the TXEN signal, the 4B/5B symbol
encoder replaces the first two nibbles of the preamble
from the MAC frame with a /J/K code-group pair (11000
10001) start-of-stream delimiter (SSD). The symbol
encoder then replaces subsequent 4B codes with cor-
responding 5B symbols. Following negation of the
TXEN signal, the encoder substitutes the first two idle
symbols with a /T/R code-group pair (01101 00111)
end-of-stream delimiter (ESD) then continuously injects
idle symbols into the transmit data stream until the next
transmit packet is detected.
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Lucent Technologies Inc.