dm9302 Davicom Semiconductor, Inc., dm9302 Datasheet - Page 53

• Manufacturer Part Number: dm9302
• Description: 10/100mbps Ethernet Fiber/twisted Pair Media Converter With Local Bus
• Manufacturer: Davicom Semiconductor, Inc.

9.3 Internal PHY functions
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
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 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.
Preliminary datasheet
DM9302-15-DS-P01
July 30, 2009
9.3.1 100Base-TX Operation
9.3.1.1 4B5B Encoder
9.3.1.2 Scrambler
10/100Mbps Ethernet Fiber/Twisted Pair Media Converter with Local bus
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 randomization to decrease
radiated emissions at critical frequencies.
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
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.
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.
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.
9.3.1.3 Parallel to Serial Converter
9.3.1.4 NRZ to NRZI Encoder
9.3.1.5 MLT-3 Converter
9.3.1.6 MLT-3 Driver
drives
either
side
of
DM9302
the
transmit
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