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GE 8B/10B Coding
GMII
Only used
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256 code groups
by
1000BaseX
8 x 125 Mbit/s
PCS
1024 code groups
8B/10B Encoder/Decoder
125 million code
groups per
second
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PMA
1250 Mbaud
(C) Herbert Haas
2005/03/11
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8B10B block coding is very similar to 4B5B block coding but allows fully
balanced 10-bit codewords. Actually, there are not enough balanced 10-bit
codewords available. Note that there are 256 8-bit codewords which need to be
mapped on 1024 10-bit codewords. But instead of using a fully balanced 10-bit
codeword for each 8-bit codeword, some 8-bit codewords are represented by two
10-bit codewords, which are sent in an alternating manner. That is, both
associated 10-bit words are bit-complementary.
Again, the signaling overhead is 12.5%, that is 1250 Mbaud is necessary to
transmit a bit stream of 1000 Mbit/s.
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