AN985B/BX
Functional Descriptions
7.4.2
Transceiver Operation
The transceiver portion of the AN985B/BX, integrates the IEEE802.3u compliant functions of PCS (physical coding
sub-layer), PMA (physical medium attachment) sub-layer, PMD (physical medium dependent) sub-layer for
100BASE-TX, the IEEE802.3 compliant functions of Manchester encoding/decoding and a transceiver for
10BASE-T. All the functions and operation schemes are described in the following sections:
7.4.2.1
100BASE-TX Transmit Operation
Regarding the 100BASE-TX transmission, the transceiver provides transmission functions PCS, PMA, and PMD
for encoding of MII data nibbles to five-bit code-groups (4B/5B), scrambling, serialization of scrambled code-
groups, converting the serial NRZ code into NRZI code, converting the NRZI code into MLT3 code, and then
driving the MLT3 code into the category 5 Unshielded Twisted Pair cable through an isolation transformer with the
turns ratio of 1:1.
Data Code-Groups Encoder
In normal MII mode application, the transceiver receives nibble type 4B data via the TxD0~3 inputs of the MII.
These inputs are sampled by the transceiver on the rising edge of Tx-clk and passed to the 4B/5B encoder to
generate the 5B code-group used by 100BASE-TX.
Idle Code-Groups
In order to establish and maintain the clock synchronization, the transceiver needs to keep transmitting signals to
medium. The transceiver will generate Idle code-groups for transmission when there is no real data MAC wants
to send.
Start-of-Stream Delimiter-SSD (/J/K/)
In a transmission stream, the first 16 nibbles are MAC preamble. In order to let a partner delineate the boundary
of a data transmission sequence and to authenticate carrier events, the transceiver will replace the first 2 nibbles
of the MAC preamble with /J/K/ code-groups.
End-of-Stream Delimiter-ESD (/T/R/)
In order to indicate the termination of the normal data transmissions, the transceiver will insert 2 nibbles of /T/R/
code-group after the last nibble of FCS.
Scrambling
All the encoded data (including the idle, SSD, and ESD code-groups) is passed to data scrambler to reduce the
EMI and spread the power spectrum using a 10-bit scrambler seed loaded at the beginning.
Data Conversion of Parallel to Serial, NRZ to NRZI, NRZI to MLT3
After being scrambled, the transmission data with 5B type in 25 MHz will be converted to a serial bit stream in 125
MHz by the parallel to serial function. After serialization, the transmission serial bit stream will be further converted
from NRZ to NRZI format. After NRZI is converted, the NRZI bit stream is passed through MLT3 encoder to
generate the TP-PMD specified MLT3 code. With this MLT3 code, it lowers the frequency and reduces the energy
of the transmission signal in the UTP cable and also makes the system easy to meet the FCC specification of EMI.
Wave-Shaper and Media Signal Driver
In order to reduce the energy of the harmonic frequency of transmission signals, the transceiver provides the
wave-shaper prior to the line driver to smoothen but keep symmetric the rising/falling edge of transmission signals.
The wave-shaped signals including the 100BASE-TX and 10BASE-T both are passed to the same media signal
driver. This design can simplify the external magnetic connection with a single one.
Data Sheet
26
Rev. 1.51, 2005-11-30
INFINEON [ Infineon ]
