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Overview
j
Bit
9
Figure B-2. Encoded Transmission Character Bit Ordering
B.1.1 Naming Transmission Characters
Transmission characters are given names based on the type of data in the byte and the bit
values of the character. Two types of transmission characters are specified: data and special.
Data characters are labeled "D" characters and special characters are labeled "K"
characters. Each transmission character has a bit value and a corresponding decimal value.
These elements are combined to provide each character with a name, see Table B-1.
H G F
0 0 1
D28.1 = Data name assigned to this data byte if it is a data character.
K28.1 = Data name assigned to this data byte if it is a special character.
B.1.2 Encoding
Following is a simplified sequence of steps in 8B/10B coding:
1. An 8-bit block of unencoded data (a transmission character) is picked up by a
transmitter.
2. The transmission character is broken into sub-blocks of three bits and five bits. The
letters H G and F comprise the 3-bit block, and the letters E D C B and A comprise
the 5-bit block.
3. The 3-bit and 5-bit sub-blocks pass through a 3B/4B encoder and a 5B/6B encoder,
respectively. A bit is added to each sub-block, such that the transmission character
is encoded and expanded to a total of 10-bits.
4. At the time the character is expanded into 10 bits, it is also encoded into the proper
running disparity, either positive (RD+) or negative (RD-) depending on certain
calculations (see Section B.1.3, "Calculating Running Disparity"). At start-up, the
transmitter assumes negative running disparity.
B-2
MC92603 Quad Gigabit Ethernet Transceiver Reference Manual
One coded transmission character (Byte)
h
g
f
Bit
Bit
Bit
8
7
6
Table B-1. Components of a Character Name
E D C B A
1 1 1 0 0
1
28
D or K
i
e
d
c
Bit
Bit
Bit
Bit
5
4
3
2
8B/10B notation
Data bit value
Decimal value of the bit value
Kind of transmission character
b
a
Bit
Bit
1
0
↑
lsb
MOTOROLA
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