GE 8B/10B Coding

GMII

Only used

256 code groups 1 1 1 1 1 1 1 1by 1000BaseX

8 x 125 Mbit/s

PCS

1024 code groups

125 million code

groups per

second

8B/10B Encoder/Decoder

1 1 1 1 1 1 1 1 1 1

1250 Mbaud

PMA

 

 

 

 

(C) Herbert Haas 2005/03/11

16

 

 

 

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.

16