ICS1893CF datasheet(32/126 Pages) ICST

32 / 126 page

ICS1893CF, Rev. F, 03/01/07

Mar. 2007

Chapter 6 Functional Blocks

ICS1893CF Data Sheet - Release

6.3.6 4B/5B Encoding/Decoding

The 4B/5B encoding methodology maps each 4-bit nibble to a 5-bit symbol (also called a “code group”).

There are 32 five-bit symbols, which include the following:

• Of the 32 five-bit symbols, 16 five-bit symbols are required to represent the 4-bit nibbles.

• The remaining 16 five-bit symbols are available for control functions. The IEEE Standard defines 6

symbols for control, and the remaining 10 symbols of this grouping are invalid. The 6 control symbols

include the following:

– /H/, which represents a Halt, also used to signify a Transmit Error

– /I/, which represents an IDLE

– /J/, which represents the first symbol of the Start-of-Stream Delimiter (SSD)

– /K/, which represents the second symbol of the Start-of-Stream Delimiter (SSD)

– /T/, which represents the first symbol of the End-of-Stream Delimiter (ESD)

– /R/, which represents the second symbol of the End-of-Stream Delimiter (ESD)

If the ICS1893CF PCS receives:

– One of the 10 undefined symbols, it sets its QuickPoll Detailed Status Register’s Invalid Symbol bit

(bit 17.7) to logic one.

– A Halt symbol, it sets the Halt Symbol Detected bit in its QuickPoll Detailed Status Register (bit 17.6)

to logic one.

Note: An STA can force the ICS1893CF to transmit symbols that are typically classified as invalid, by

both (1) setting the Extended Control Register’s Transmit Invalid Codes bit (bit 16.2) to logic one

and (2) asserting the associated TXER signal. For more information, see Section 7.11.7, “Invalid

Error Code Test (bit 16.2)”.

6.4 Functional Block: 100Base-TX TP-PMD Operations

The ICS1893CF supports both 10Base-T and 100Base-TX operations. For 100Base-TX operations, the

TP-PMD module performs stream-cipher scrambling/descrambling and MLT-3 encoding/decoding (3-level,

multi-level transition) in compliance with the ANSI Standard X3.263: 199X FDDI TP-PMD as defined in the

specification for 100Base-TX Twisted-Pair Physical Media Dependent (TP-PMD) Sublayer. The

ICS1893CF’s TP-PMD also performs DC restoration (that is, baseline wander correction) and adaptive

equalization on the received signals.

Note:

1. For an overview of 100Base-TX operations, see Section 4.5, “100Base-TX Operations”.

2. For more information on the Twisted-Pair Interface, see Section 5.3, “Twisted-Pair Interface”.

6.4.1 100Base-TX Operation: Stream Cipher Scrambler/Descrambler

When the ICS1893CF is operating in 100Base-TX mode, it employs a stream cipher

scrambler/descrambler that complies with the ANSI Standard X3.263: 199X FDDI TP-PMD. The purpose of

the stream cipher scrambler is to spread the transmission spectrum to minimize electromagnetic

compatibility problems. The stream cipher descrambler restores the received serial bit stream to its

unscrambled form.

The ICS1893CF “seeds” (that is, initializes) the Transmit Stream Cipher Shift register by using the

ICS1893CF PHY address from Table 7-16, which minimizes crosstalk and noise in repeater applications.

The MAC Interface bypasses the stream cipher scrambler/descrambler when in the 100M Symbol Interface

mode.

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