DM9000BEP DAVICOM [Davicom Semiconductor, Inc.], DM9000BEP Datasheet - Page 39

• Manufacturer Part Number: DM9000BEP
• Description: Ethernet Controller With General Processor Interface
• Manufacturer: DAVICOM [Davicom Semiconductor, Inc.]

9.5 100Base-TX Operation
The transmitter section contains the following
functional blocks:
- 4B5B Encoder
- Scrambler
- Parallel to Serial Converter
- NRZ to NRZI Converter
- NRZI to MLT-3
- MLT-3 Driver
9.5.1 4B5B Encoder
The 4B5B encoder converts 4-bit (4B) nibble data
generated by the MAC Reconciliation Layer into a
5-bit (5B) code group for transmission, see reference
Table 1. This conversion is required for control and
packet data to be combined in code groups. The
4B5B encoder substitutes 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 the 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 DM9000B includes a Bypass 4B5B conversion
option within the 100Base-TX Transmitter for support
of applications like 100 Mbps repeaters which do not
Require 4B5B conversion.
9.5.2 Scrambler
The scrambler is required to control the radiated
emissions (EMI) by spreading the transmit energy
across the frequency spectrum at the media
connector and on the twisted pair cable in
100Base-TX operation.
Final
Version: DM9000B-13-DS-F02
June 4, 2009
Ethernet Controller with General Processor Interface
By scrambling the data, the total energy presented to
the cable is randomly distributed over a wide
frequency range. Without the scrambler, energy levels
on the cable could peak beyond FCC limitations at
frequencies related to the repeated 5B sequences,
like the continuous transmission of IDLE symbols.
The scrambler output is combined with the NRZ 5B
data from the code-group encoder via an XOR logic
function. The result is a scrambled data stream with
sufficient
emissions at critical frequencies.
9.5.3 Parallel to Serial Converter
The Parallel to Serial Converter receives parallel 5B
scrambled data from the scrambler, and serializes it
(converts it from a parallel to a serial data stream).
The serialized data stream is then presented to the
NRZ to NRZI encoder block
9.5.4 NRZ to NRZI Encoder
After the transmit data stream has been scrambled
and serialized, the data must be NRZI encoded for
compatibility with the TP-PMD standard, for 100Base
-TX transmission over Category-5 unshielded twisted
pair cable.
9.5.5 MLT-3 Converter
The MLT-3 conversion is accomplished by converting
The data stream output, from the NRZI encoder into
two binary data streams, with alternately phased logic
One event.
9.5.6 MLT-3 Driver
The two binary data streams created at the MLT-3
converter are fed to the twisted pair output driver,
which converts these streams to current sources and
alternately
transformer’s primary winding, resulting in a minimal
current MLT-3 signal.
randomization
drives
either
to
side
decrease
DM9000B
of
the
radiated
transmit
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