Running disparity

30 December 2020

The cumulative number of ones minus the cumulative number of zeros that have been transmitted on the ARINC 818 serial link. Each byte of data feed to the 8b/10b encoder will have two possible 10-bit output codes. Typically these codes will be one with 6 ones and 4 zeros and one with 4 ones and six zeros. (Another possibility is a neutral code with 5 ones and 5 zeros, which does not affect the running disparity.) For each input byte, the 8b/10b encoder will choose the 10-bit code that keeps the running disparity between -1 and +1.