Datasheet

DP83630
www.ti.com SNLS335B –OCTOBER 2010–REVISED APRIL 2013
7.1.1 Code-Group Encoding and Injection
The code-group encoder converts 4-bit (4B) nibble data generated by the MAC into 5-bit (5B) code-groups
for transmission. This conversion is required to allow control data to be combined with packet data code-
groups. Refer to Table 7-1 for 4B to 5B code-group mapping details.
The code-group encoder substitutes the first 8-bits of the MAC preamble with a J/K code-group pair
(11000 10001) upon transmission. The code-group 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 Transmit Enable signal from the MAC, the code-group encoder injects the T/R code-group
pair (01101 00111) indicating the end of the frame.
After the T/R code-group pair, the code-group encoder continuously injects IDLEs into the transmit data
stream until the next transmit packet is detected (reassertion of Transmit Enable).
7.1.2 Scrambler
The scrambler is required to control the radiated emissions at the media connector and on the twisted pair
cable (for 100BASE-TX applications). By scrambling the data, the total energy launched onto the cable is
randomly distributed over a wide frequency range. Without the scrambler, energy levels at the PMD and
on the cable could peak beyond FCC limitations at frequencies related to repeating 5B sequences (i.e.,
continuous transmission of IDLEs).
The scrambler is configured as a closed loop linear feedback shift register (LFSR) with an 11-bit
polynomial. The output of the closed loop LFSR is X-ORd with the serial NRZ data from the code-group
encoder. The result is a scrambled data stream with sufficient randomization to decrease radiated
emissions at certain frequencies by as much as 20 dB. The DP83630 uses the PHY_ID (pins PHYAD
[4:0]) to set a unique seed value.
7.1.3 NRZ to NRZI Encoder
After the transmit data stream has been serialized and scrambled, the data must be NRZI encoded in
order to comply with the TP-PMD standard for 100BASE-TX transmission over Category-5 Unshielded
twisted pair cable. There is no ability to bypass this block within the DP83630. The NRZI data is sent to
the 100 Mb Driver. In addition, this module creates an encoded MLT value for use in 100 Mb Internal
Loopback.
7.1.4 Binary to MLT-3 Convertor
The Binary to MLT-3 conversion is accomplished by converting the serial binary data stream output from
the NRZI encoder into two binary data streams with alternately phased logic one events. These two binary
streams are then fed to the twisted pair output driver which converts the voltage to current and alternately
drives either side of the transmit transformer primary winding, resulting in a minimal current MLT-3 signal.
The 100BASE-TX MLT-3 signal sourced by the PMD Output Pair common driver is slew rate controlled.
This should be considered when selecting AC coupling magnetics to ensure TP-PMD Standard compliant
transition times (3 ns < Tr < 5 ns).
The 100BASE-TX transmit TP-PMD function within the DP83630 is capable of sourcing only MLT-3
encoded data. Binary output from the PMD Output Pair is not possible in 100 Mb/s mode.
7.2 100BASE-TX RECEIVER
The 100BASE-TX receiver consists of several functional blocks which convert the scrambled MLT-3 125
Mb/s serial data stream to synchronous 4-bit nibble data that is provided to the MII. Because the
100BASE-TX TP-PMD is integrated, the differential input pins, RD±, can be directly routed from the AC
coupling magnetics.
See Figure 7-2 for a block diagram of the 100BASE-TX receive function. This provides an overview of
each functional block within the 100BASE-TX receive section.
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