ARINC 429 Word Builder
Build a 429 word from label, SDI, SSM and data — parity computed.
Parity is computed here, so a word with the wrong parity cannot be produced.
This tool assembles a 32-bit ARINC 429 word. Enter the octal label, the SDI, the SSM for your data type and the data itself, and it returns the word in hex with odd parity already computed — then decodes it straight back so you can check the fields landed where you meant. Reference: label 205 with BNR data 400 and SSM 3 builds a word whose parity is fixed for you.
How it works
Assembling a 429 word by hand goes wrong in two places. The first is parity: it is odd across all thirty-two bits, so it depends on every other field and has to be recomputed whenever any of them changes. This builder computes it rather than accepting it, which means a word with the wrong parity is not something it can produce.
The second is the label. Its bits run opposite to the rest of the word, and published sources disagree about which end holds the octal number's most significant bit — so the same label builds two different words depending on the convention. Rather than pick one quietly, the builder makes it a choice and prints the other reading beside the result. Decoding the built word back on the spot is the cheapest way to confirm you chose correctly before anything reaches a bus.
Worked example
→ parity computed on bit 32
decodes back as label 205, SDI 2, SSM 3
same bits read the other way round → label 241
Fields you supply
| Parameter | Value | Notes |
|---|---|---|
| Label | 3-digit octal | bit order is a choice |
| SDI | 0–3 | bits 9–10 |
| Data | bits 11–29 | BNR signed, bit 29 is sign |
| BCD | up to 5 digits | top digit is 3 bits |
| SSM | 0–3 | meaning follows the format |
| Parity | computed | odd, not an input |
Field map and parity cross-checked against the AIM ARINC 429 tutorial, the GE Intelligent Platforms / Condor-Ballard protocol tutorial, and the Holt HI-35850 datasheet. Label assignments and equipment IDs are deliberately not published here.
FAQ
▸Do I set the parity bit myself?
No, and you cannot. Bit 32 is computed from the other 31 bits every time, so there is no input for it and no way to emit a word whose parity is wrong. Parity on ARINC 429 is odd across the whole word.
▸Which label bit order should I choose?
Whichever your equipment documentation uses. Public sources number the label bits in opposite directions, so the same octal label produces two different words depending on the convention. The builder shows the other reading beside the result, so you can confirm you picked the one your ICD means before putting the word on a bus.
▸What goes in the data field?
For BNR, a signed value occupying bits 29 to 11, where bit 29 is the sign — the scale that turns it into knots or degrees comes from the parameter's full-scale range in your ICD, not from the word. For BCD, up to five digits with the most significant one limited to three bits. Switching format changes the input accordingly.
▸Why does the SSM list change with the format?
Because the sign/status matrix means different things per data type. BNR reports failure warning, no computed data, functional test or normal operation; BCD carries sign and direction alongside the same failure states; discrete words use their own reading. The dropdown shows the readings for the format you selected rather than one merged list.
▸Can I look up what a label means?
Not here. Label assignments live in the ARINC 429 specification and in per-aircraft interface control documents, which are controlled, paid documents. Publishing a guessed table would produce words that look right and are not, so the builder takes the octal label you supply and leaves the meaning to your ICD.
▸Is anything uploaded?
No. The word is assembled in your browser.