STE10A Datasheet, PDF (21/82 Pages) STMicroelectronics – PCI 10/100 Ethernet controller with integrated PHY (3.3V)

STE10/100A
Functional description
3.5.2
Collision handling
The scheduling of re-transmissions are determined by a controlled randomization process
called “truncated binary exponential back-off”. At the end of enforcing a collision (jamming),
the STE10/100A delays before attempting to re-transmit the packet. The delay is an integer
multiple of slot time. The number of slot times to delay before the nth re-transmission
attempt is chosen as a uniformly distributed integer r in the range:
0 · r < 2^k where k = min(n, 10)
Transceiver operation
The transceiver portion of the ste10/100a integrates the ieee802.3u compliant functions of
PCS (physical coding sub-layer), PMA (physical medium attachment) sub-layer, and PMD
(physical medium dependent) sub-layer for 100base-tx, and the ieee802.3 compliant
functions of manchester encoding/decoding and transceiver for 10base-t. All the functions
and operating schemes are described in the following sections.
100BASE-TX transmit operation
For 100BASE-TX transmissions, the STE10/100A transceiver provides the transmission
functions of PCS, PMA, and PMD for encoding of MII data nibbles into 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.
Recommended transformers
HB626-1 from transpower technologies, 9410 prototype drive, suite #1, Reno, NV 89511.
Tel: [phone] and H1102 from pulse engineering Inc., 12220 World Trade Drive, San
Diego, CA92128. Tel: [phone].
Data code-groups encoder
In normal MII mode applications, 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 must keep
transmitting signals to medium. The transceiver will generate Idle code-groups for
transmission when there is no actual data to be sent by MAC.
Start-of-stream delimiter-SSD (/J/K/)
In a transmission stream, the first 16 nibbles comprise the MAC preamble. In order to let a
network 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.
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