DM9620 DAVICOM [Davicom Semiconductor, Inc.], DM9620 Datasheet - Page 55

• Manufacturer Part Number: DM9620
• Description: USB2.0 to 10/100M Fast Ethernet Controller
• Manufacturer: DAVICOM [Davicom Semiconductor, Inc.]

7.2.10 100Base-TX Receiver
The 100Base-TX receiver contains several function
blocks that convert the scrambled 125Mb/s serial
data to synchronous 4-bit nibble data that is then
provided to the MII.
The receive section contains the following functional
blocks:
- Signal Detect
- Digital Adaptive Equalization
- MLT-3 to Binary Decoder
- Clock Recovery Module
- NRZI to NRZ Decoder
- Serial to Parallel
- Descrambler
- Code Group Alignment
- 4B5B Decoder
7.2.11 Signal Detect
The signal detect function meets the specifications
mandated by the ANSI XT12 TP-PMD 100Base-TX
Standards for both voltage thresholds and timing
parameters.
7.2.12 Adaptive Equalization
When transmitting data at high speeds over copper
twisted pair cable, attenuation based on frequency
becomes a concern. In high speed twisted pair
signaling, the frequency content of the transmitted
signal can vary greatly during normal operation based
on the randomness of the scrambled data stream.
This variation in signal attenuation caused by
frequency variations must be compensated for to
ensure the integrity of the received data. In order to
ensure quality transmission when employing MLT-3
encoding, the compensation must be able to adapt to
various cable lengths and cable types depending on
the installed environment. The selection of long cable
lengths for a given implementation, requires
significant compensation which will be over-kill in a
situation that includes shorter, less attenuating cable
lengths. Conversely, the selection of short or
intermediate cable lengths requiring less
compensation will cause serious under-compensation
for longer length cables. Therefore, the compensation
or equalization must be adaptive to ensure proper
Preliminary
Version: DM9620 -15-DS-P02
February 20, 2012
conditioning of the received signal independent of the
cable length.
7.2.13 MLT-3 to NRZI Decoder
The DM9620 decodes the MLT-3 information from
the Digital Adaptive Equalizer into NRZI data. The
relationship between NRZI and MLT-3 data is shown
in figure 4.
7.2.14 Clock Recovery Module
The Clock Recovery Module accepts NRZI data from
the MLT-3 to NRZI decoder. The Clock Recovery
Module locks onto the data stream and extracts the
125Mhz reference clock. The extracted and
synchronized clock and data are presented to the
NRZI to NRZ Decoder.
7.2.15 NRZI to NRZ
The transmit data stream is required to be NRZI
encoded in for compatibility with the TP-PMD
standard for 100Base-TX transmission over
Category-5 unshielded twisted pair cable. This
conversion process must be reversed on the receive
end. The NRZI to NRZ decoder, receives the NRZI
data stream from the Clock Recovery Module and
converts it to a NRZ data stream to be presented to
the Serial to Parallel conversion block.
7.2.16 Serial to Parallel
The Serial to Parallel Converter receives a serial data
stream from the NRZI to NRZ converter, and converts
the data stream to parallel data to be presented to the
descrambler.
7.2.17 Descrambler
Because of the scrambling process required to
control the radiated emissions of transmit data
streams, the receiver must descramble the receive
data streams. The descrambler receives scrambled
parallel data streams from the Serial to Parallel
converter, descrambles the data streams, and
presents the data streams to the Code Group
alignment block.
USB2.0 to Fast Ethernet Controller
DM9620
55