ST802RT1AFR datasheet(38/58 Pages) STMICROELECTRONICS

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Device operation

ST802RT1A, ST802RT1B

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Doc ID 17049 Rev 1

Device operation

The ST802RT1x includes a 10/100 Base-T Ethernet transceiver with MII, RMII interfaces for

data and control from/to the station management entity (STE). The ST802RT1x integrates

the IEEE802.3u compliant functions of PCS (physical coding sub-layer), PMA (physical

medium attachment), and PMD (physical medium dependent) for 100Base-TX, and the

IEEE802.3 compliant functions of manchester encoding/decoding and transceiver for

10Base-T. IEEE standard auto-negotiation functions are also supported. Media independent

interface (MII) is a 4-bit interface transferring 10 Mbit data using a 2.5 MHz clock and 100

Mbit data using a 25 MHz clock. RMII (reduced media independent interface) is a low pin

count alternative capable of transferring 10 and 100 Mbit dibits data using a 50 MHz

reference clock. All the functions and operation schemes are described in the sections that

follow.

7.1

100Base-TX transmit operation

In 100Base-TX transmission, the device provides the transmission functions of 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 a turn ratio of 1.414:1.

Data code-groups encoder: In normal MII mode application, the device receives nibble type

4B data via the TxD0~3 inputs of the MII. These inputs are sampled by the device 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 device

needs to keep transmitting signals to the medium. The device generates idle code-groups

for transmission when there is no data sent by the MAC.

Start-of-stream delimiter-SSD (/J/K/): In a transmission stream, the first 16 nibbles are SFD

(1 byte) and MAC preamble (7 byte). In order to let partner delineate the boundary of a data

transmission sequence and to authenticate carrier events, the device replaces 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 device inserts 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 the data scrambler to reduce the EMI and spread the power spectrum using a 10-bit

scrambler seed loaded at the beginning.

Parallel-to-serial data conversion, NRZ to NRZI, NRZI to MLT3: after being scrambled, the

transmission data with 5B type at 25 MHz is converted to serial bit stream at 125 MHz by the

parallel-to-serial function. After being serialized, the transmission serial bit stream is further

converted from NRZ to NRZI format. This NRZI conversion function can be bypassed if bit 7

of the RN13 register is cleared as 0. After being NRZI converted, the NRZI bit stream is

passed through the MLT3 encoder to generate the TP-PMD specified MLT3 code. The MLT3

code lowers the frequency and reduces the energy of the transmission signal in the UTP

cable and also allows the system to meet the FCC specification for EMI.

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