ICS1893AGILF datasheet(43/135 Pages) ICST

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Chapter 7 Functional Blocks

ICS1893AG, Rev. A 04/14/05

April, 2005

ICS1893AG Data Sheet - Preliminary

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

The ICS1893AG 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

ICS1893AG’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 5.5, “100Base-TX Operations”.

2. For more information on the Twisted-Pair Interface, see Section 6.3, “Twisted-Pair Interface”.

7.4.1 100Base-TX Operation: Stream Cipher Scrambler/Descrambler

When the ICS1893AG 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 ICS1893AG “seeds” (that is, initializes) the Transmit Stream Cipher Shift register by using the

ICS1893AG PHY address from Table 8-16, which minimizes crosstalk and noise in repeater applications.

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

Symbol Interface mode.

7.4.2 100Base-TX Operation: MLT-3 Encoder/Decoder

When operating in the 100Base-TX mode, the ICS1893AG TP-PMD sublayer employs an MLT-3 encoder

and decoder. During data transmission, the TP-PMD encoder converts the NRZI bit stream received from

the PMA sublayer to a 3-level Multi-Level Transition code. The three levels are -1, 0, and +1. The results of

MLT-3 encoding provide a reduction in the transmitted energy over the critical frequency range from 20

MHz to 100 MHz. The TP-PMD MLT-3 decoder converts the received three-level signal back to an NRZI bit

stream.

7.4.3 100Base-TX Operation: DC Restoration

The ICS1893AG’s 100Base-TX operations uses a stream-cipher scrambler to minimize peak amplitudes in

the frequency spectrum. However, the nature of the stream cipher and MLT-3 encoding is such that long

sequences of consecutive zeros or ones can exist. These unbalanced data patterns produce an

undesirable DC component in the data stream known as ‘baseline wander’.

Baseline wander adversely affects the noise immunity of the receiver, because the ‘baseline’ signal moves

or ‘wanders’ from its nominal DC value. The ICS1893AG uses a unique technique to restore the DC

component ‘lost’ by the medium. As a result, the design is very robust, immune to noise and independent

of the data stream.

ICS1893AGILF Datasheet(PDF) 43 Page - Integrated Circuit Systems