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MIL-STD-1553

MIL-STD-1553 is a 1 Mb/s Manchester II encoded, transformer-coupled bus used in aircraft avionics, spacecraft and ground military vehicles. A Bus Controller issues Command Words; a Remote Terminal answers with a Status Word and whatever Data Words the command asked for. Command and Status words are indistinguishable on the wire — which is which is resolved by tracking the message.

Probing. The bus is differential and transformer-coupled, while the analyzer measures one wire against ground, so set the threshold to 20–30 % of the peak amplitude rather than 0 V — the standard tolerates a residual level between messages that a comparator sitting on zero will chatter through. Check which of the two wires the measured signal is on: a signal taken from the inverted wire cannot be decoded, and the report says so rather than inventing words.

Decode Settings

Decode Settings

MIL-STD-1553 Decode Settings
  • View: Which layer the waveform strip shows — Field (Sync, RT Address, T/R, SubAddress, Word Count …), Word (Command / Status / Data), or Transfer (one block per transfer). All three come from the same analysis; open a second instance of the decode on the same capture to see more than one layer at once. Default: Field.
  • Tolerance: How much bit-time deviation to accept. A receiver must tolerate ±150 ns of zero-crossing deviation out of a 500 ns half bit, which is 30 %. Default: 30%.
  • Version: MIL-STD-1553B or MIL-STD-1553A. The two revisions differ only in what the Status Word's bits are called. Everything used to recover the bits from the waveform — the sync patterns, the Manchester decoding, the 16 data bits and the parity bit — is the same in both, so this setting changes the names in the report and nothing else. Default: MIL-STD-1553B.
  • Response From / Response To: The window a Remote Terminal must answer in. The measured time is always shown; these bounds decide when it is flagged. Default: 4 us / 12 us.
  • Gap Minimum: The shortest intermessage gap accepted between transfers. Default: 4 us.

Result

MIL-STD-1553 Result

Field view — a BC-to-RT transfer with its Status Word response

Errors are reported at two levels. Word level: Invalid Sync, Manchester Error and Parity Error. Transfer level: Bad Word Count, Address Mismatch, Non-contiguous Data, Response Time and Intermessage Gap. Each fault is flagged once, on the field it is about.

When most words fail to decode the report opens with a warning instead of listing words that were never really there — check the probe connection, the threshold, and which wire of the pair is being probed.