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I am reading 1553 bus protocol documentation and it says that ME bit is set in case data words are invalid. But what happens if the receive command word itself is invalid? Will the remote terminal ignore it or will it set ME bit even in this case?

Kishan Kumar
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  • Note to potential closers: Just because *you* may not be familiar with the 1553 bus protocol documentation and terminology, doesn't mean there's anything wrong with the question. The question is fine and perfectly clear as-is! – Kuba hasn't forgotten Monica Apr 15 '22 at 17:02
  • if you think about it logically, the remote terminal should always report any detected error in data ... silently ignoring a command could easily have disastrous consequences, especially in a military aircraft – jsotola Apr 15 '22 at 17:34
  • @jsotola In the 1553 protocol, a status word is expected within 14us and if it does not retries happen. So this way disaster is avoided. But I am still not sure whether it is a silent ignore or sts word is sent back. – Kishan Kumar Apr 16 '22 at 13:14

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Sounds like you are suggesting a BCRT (rcv cmd).

If the command word is validated but any data word is invalidated, all of the data should be ignored by the receive RT.

If the Command word is invalid, that means that something was wrong with the waveform or parity so it could not be 100% validated. In this case it was not a real command and the RT cannot recognize it (or any other RT). In this case it should be completely ignored, no status response. Basically just treated as noise. If the command word is validated, correctly formed and good parity to an RT that is on the bus, it should be responded to by the RT.

The RT would set the ME bit in the status response word if the command word is valid, but "illegalized".

If any one of the data words that come along with the valid BCRT command word has problems, is not 100% validated, then the RT should set the ME bit, but not use any of the data.

Bill Tilman
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