82562GT Datasheet, PDF(20/46 Page) Intel Corporation – 10/100 Mbps Platform LAN Connect (PLC)

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82562GT Datasheet, PDF (20/46 Pages) Intel Corporation – 10/100 Mbps Platform LAN Connect (PLC)

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82562GT â Networking Silicon

5.1.1.2

5.1.1.3

Symbol

5B Symbol Code

4B Nibble Code

11000

10001

01101

00111

00000

00001

00010

00011

00100

00101

00110

01000

01100

10000

11001

1st Start of Packet Symbol

0101

2nd Start of Packet Symbol

0101

1st End of Packet Symbol

2nd End of Packet Symbol

and Flow Control

INVALID

Flow Control S

INVALID

100BASE-TX Scrambler and MLT-3 Encoder

Data is scrambled in 100BASE-TX in order to reduce electromagnetic emissions during long

transmissions of high-frequency data codes. The scrambler logic accepts 5 bits from the 4B/5B

encoder block and presents the scrambled data to the MLT-3 encoder. The 82562GT implements

the 11-bit stream cipher scrambler as adopted by the ANSI XT3T9.5 committee for UTP operation.

The cipher equation used is:

X[n] = X[n-11] + X[n-9] (mod 2)

The MLT-3 encoder receives the scrambled Non-Return to Zero (NRZ) data stream from the

scrambler and encodes the stream into MLT-3 for presentation to the driver. MLT-3 is similar to

NRZ1 coding, but three levels are output instead of two. The three output levels are positive,

negative and zero. When an NRZ â0â arrives at the input of the encoder, the last output level is

maintained (either positive, negative or zero). When an NRZ â1â arrives at the input of the encoder,

the output steps to the next level. The order of steps is negative-zero-positive-zero which continues

periodically. Refer to IEEE 802.3 Specification for details.

100BASE-TX Transmit Framing

The 82562GT does not differentiate between the fields of the MAC frame containing preamble,

start of frame delimiter, data and Cyclic Redundancy Check (CRC). The 82562GT encodes the first

byte of the preamble as the âJKâ symbol, encodes all other pieces of data according to the 4B/5B

lookup table, and adds the âTRâ code after the end of the packet. The 82562GT scrambles and

serializes the data into a 125 Mbps stream, encodes it as MLT-3, and drives it onto the wire.

Datasheet

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