CCIR 476 is a character encoding used in radio data protocols such as SITOR, AMTOR and Navtex.
The SITOR protocol uses the additional three code points (denoted as SIA, SIB and RPT below) for idle, phasing, and repeat requests.
[1] In addition, some of the ordinary characters are reused as control signals.
[2] In these tables, the hexadecimal code values are converted from a binary representation, with 1 being mark, 0 being space, and the most significant bit given first.
The international version of ITA2 is used here; note also the added non-ITA2 codes SIA, SIB and RPT, used by SITOR.