
MOTOROLA
Appendix B. 8B/10B Coding Scheme
B-1
Appendix B
8B/10B Coding Scheme
The MC92603 provides fibre channel-specific 8B/10B encoding and decoding based on the
FC-1 fibre channel standard. Given 8 bits entering a channel, the 8B/10B encoding converts
them to 10 bits thereby increasing the transition density of the serially transmitted signal.
B.1 Overview
The FC-1 standard applies an algorithm that ensures that no more than five 1’s or 0’s are
transmitted consecutively, giving a transition density equal to 2.5 for each 10 bit data block.
Such a density ensures proper DC balance across the link and is sufficient for good clock
recovery.
In the 8B/10B notation scheme, bytes are referred to as transmission characters, and each
bit is represented by letters. Unencoded bits, the 8 bits that have not passed through a
8B/10B encoder, are represented by letters “A” through “H”, which are bits 0 through7.
Figure B-1. Unencoded Transmission Character Bit Ordering
Encoded bits, those that have passed through an encoder, are represented with the letters
“a” through “j”, representing bits 0–9 respectively. Character (bit) ordering in the fibre
channel nomenclature is little-endian, with “a” being the least significant bit in a byte.
One unencoded transmission character (Byte)
H
G
F
E
D
C
B
A
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
↑
lsb
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