DM9161CI DAVICOM [Davicom Semiconductor, Inc.], DM9161CI Datasheet - Page 17

• Manufacturer Part Number: DM9161CI
• Description: Industrial-Temperature 10/100 Mbps Fast Ethernet Physical Layer Single Chip Transceiver
• Manufacturer: DAVICOM [Davicom Semiconductor, Inc.]

The block diagram in figure 7-3 provides an overview of the
functional blocks contained in the transmit section.
The transmitter section contains the following functional
blocks:
- 4B5B Encoder
- Scrambler
- Parallel to Serial Converter
- NRZ to NRZI Encoder
- NRZI to MLT-3
- MLT-3 Driver
7.2.1.1 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 7-1. 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 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.
within the 100Base-TX Transmitter for support of
applications like 100 Mbps repeaters, which do not require
4B5B conversion.
7.2.1.2 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.
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The DM9161CI includes a Bypass 4B5B conversion option
10/100 Mbps Fast Ethernet Physical Layer Single Chip Transceiver
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
repeated 5B sequences like 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.
7.2.1.3 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
7.2.1.4 NRZ to NRZI Encoder
Since 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.
7.2.1.5 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 events.
7.2.1.6 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
drives either side of the transmit transformer’s primary
winding, resulting in a minimal current MLT-3 signal. Refer to
figure 7-4 for the block diagram of the MLT-3 converter.
Version: DM9161CI-DS-F01
DM9161CI
February 22, 2012
Final