ECSS-E-ST-50-12C Rev.1 introduces the concept of broadcast codes, using the control-flags described below. See ECSS-E-ST-50-12C vs ECSS-E-ST-50-12C Rev.1, what’s the difference? for more information.

A SpaceWire time-code comprises the SpaceWire ESC character followed by a single 8-bit data character. The data character contains two control-flags and a six-bit time-count. The time-code is illustrated in Figure 65. The six-bit time-count is held in the least-significant six-bits of the Time-Code (T0-T5) while the two most-significant bits (T6, T7) contain the two control-flags. The parity bit (P) in the middle of the time-code is set to one to give the correct parity.

Figure 65 SpaceWire Time-Code

The two control-flags are for general use, they do not have a specific function for time-code distribution. The only permitted value for the flags is 0b00. The other possible values are reserved.