6b8b code
The 6b8b code is a line code that maps six bits to eight bits and allows four control characters . It was invented in 2004 by Albert Xavier Widmer at IBM . With this code, every valid code word contains exactly four zeros and four ones. Each code word is thus balanced and each one-bit error leads to an invalid code word. The 6 b 8 b code is of those of the form {2n} b {2n + 2} b with n = 3 the longest possible code with these properties.
The number of possible code words is calculated as follows . The additional possible 70 - 64 = 6 code words are either prohibited or control characters. The longest sequence of the same characters results in six if two such code words follow one another that the first ends with the same three characters with which the next begins. Since such a sequence of six identical characters can only occur if exactly three at the end meet exactly three at the beginning, it is clear where the code word boundary is when such a sequence occurs. The largest possible deviation from equilibrium is 3 characters.
There is a rule-based assignment for 48 of the 62 (???) permissible code words. The remaining 22 code words, which are assigned to inputs with a high imbalance, all start with the same two bits, but can otherwise be taken from a table.