ICS1893 datasheet(45/152 Pages) ICST

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Chapter 7

Functional Blocks

ICS1893 Rev C 6/6/00

June, 2000

ICS1893 - Release

7.3.3

PCS/PMA Transmit Modules

Both the PCS and PMA sublayers have Transmit modules.

7.3.3.1

PCS Transmit Module

The ICS1893 PCS Transmit module accepts nibbles from the MAC/Repeater Interface and converts the

nibbles into 5-bit ‘code groups’(referred to here as ‘symbols’). In addition, the PCS Transmit module

performs a parallel-to-serial conversion on the symbols, and subsequently passes the resulting serial bit

stream to the PMA sublayer.

The first 16 nibbles of each MAC/Repeater Frame represent the Frame Preamble. The PCS replaces the

first two nibbles of the Frame Preamble with the Start-of-Stream Delimiter (SSD), that is, the symbols /J/K/.

After receipt of the last Frame nibble, detected when TX_EN = FALSE, the PCS appends to the end of the

Frame an End-of-Stream Delimiter (ESD), that is, the symbols /T/R/. (The ICS1893 PCS does not alter any

other data included within the Frame.)

The PCS Transmit module also performs collision detection. In compliance with the ISO/IEC specification,

when the transmission and reception of data occur simultaneously and the ICS1893 is in:

• Half-duplex mode, the ICS1893 asserts the collision detection signal (COL).

• Full-duplex mode, COL is always FALSE.

7.3.3.2

PMA Transmit Module

The ICS1893 PMA Transmit module accepts a serial bit stream from its PCS and converts the data into

NRZI format. Subsequently, the PMA passes the NRZI bit stream to the Twisted-Pair Physical Medium

Dependent (TP-PMD) sublayer.

The ICS1893 PMA Transmit module uses a digital PLL to synthesize a transmit clock from the Clock

Reference Interface. When the ICS1893 is configured for an interface that is:

• 10M MII (that is, 10Base-T), the TXCLK signal is 2.5 MHz

• 10M Serial Interface, the TXCLK signal is 10 MHz

• Either of the following, the TXCLK signal (a buffered version of the REF_IN signal) is 25 MHz:

– 100M MII (that is, 100Base-TX)

– 100M Symbol Interface

Note:

All of the TXCLK signals are derived from the REF_IN signal that goes to the digital PLL.

For the MII, for both the 10Base-T and 100Base-TX modes, the clock that is generated synchronizes

all data transfers across the MII.

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