Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
On the wikipedia page for 8b10b encoding (as of writing), the 3b4b table shows that if RD=-1, the outputs can have more 0's than 1's, and if RD=+1, it can have more 1's than 0's. This does not make sense to because if you already have too many 1's or 0's, you would not want to go more positive, or negative. Is this a mistake on the wikipedia page, or is my understanding of 8b10b wrong?
https://en.wikipedia.org/wiki/8b/10b_encoding
The standard 8b/10b encoding for Ethernet is found in IEEE 802.3 clause 36, table 36-1a:
The disparity effect of the 6b/5b part of the code and the 4b/5b part of the code have to be considered together.
For example, for input code group D0.0, if running disparity is negative we use a 6b/5b code with +2 disparity and a 4b/5b code with -1 disparity to get an overall +1 disparity for the 8b/10b encoding. (and similarly -2 and +1 disparities if RD is positive)
But for code group D17.0, we have a balanced code for the 5b/6b part and for RD- we use a +2 disparity code for the 4b/5b part or -2 if RD is positive.
So sometimes the 4b/5b code acts to restore the overall running disparity, but other times it acts to increase the running disparity, but it's balanced by the 5b/6b code.
I think the tables are incorrect and this is the correct one ,, note: the edits are in Dx4 and Dx7.
