Pathological Check Codes and the SMPTE Scrambler in the HD Age

The scrambling technique used in the SMPTE serial digital interface (SDI) standards can produce so-called pathological conditions—long runs of 1s or 0s that challenge the capabilities of the receiving equipment and may lead to bit errors if not handled correctly. This paper revisits how pathological conditions can arise and makes some new observations with respect to pathological conditions in 1.5 Gbit/s and recently-standardized 3 Gbit/s HD SDI links.