DM9601E ETC1 [List of Unclassifed Manufacturers], DM9601E Datasheet - Page 38

• Manufacturer Part Number: DM9601E
• Description: USB Ethernet MAC Controller with Intergrated 10/100 PHY
• Manufacturer: ETC1 [List of Unclassifed Manufacturers]

12. Functional Description
12.1 100Base-TX Operation
The block diagram in figure 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 Converter
- NRZI to MLT-3
- MLT-3 Driver
12.1.1 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, reference to
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 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 DM9601 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.
12.1.2 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.
38
USB to Ethernet MAC Controller with Integrated 10/100 PHY
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.
12.1.3 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
12.1.4 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.
12.1.5 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.
12.1.6 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 4 for the block
diagram of the MLT-3 converter.
Version: DM9601-DS-F01
DM9601
June 22, 2002
Final