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How can I encode an altitude (ft) in ARINC429? I didn't understand if I just need to transform it in binary number and then use the "Bipolar Return-to-Zero". Like for example with an altitude of 25 000 ft.

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    $\begingroup$ Which A429 label are you asking about? there are numerous 'altitude' labels with different coding (BCD, BNR), different ranges, and different resolutions. It also depends on what equipment is the source of the data (equipment code). $\endgroup$ – Gerry Oct 24 '17 at 11:56
  • $\begingroup$ I just need examples for some of them. Cause I don't need to know specifically. So you can choose the labels and equipment code you want for both BCD and BNR codings. In this way I will have a better understanding. Thank you very much! $\endgroup$ – Hari Seldon Oct 24 '17 at 13:26
  • $\begingroup$ Bipoloar Return to Zero is related to actually transmitting the label. It does not affect the encoding of the label. What device are you trying to transmit from? $\endgroup$ – selectstriker2 Oct 24 '17 at 14:16
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From ARINC 429, Attachment 6:

Label 025, Selected Altitude (BCD)
Five binary coded decimals. Range is up to 50000. Resolution is 1 foot.

Bit 29 (MSC) ------------------------------ Bit 11 (LSC)
4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1

1 0 0 | 0 0 0 1 | 0 0 0 0 | 0 0 0 0 | 0 0 0 0
The above line codes to 41000 ft.
Note: Negative sign is annunciated in the sign/status matrix.

Label 102, Selected Altitude (BNR) 16 bits of data. Range of 65536. Resolution (value of LSB) is 1 foot.

Bit 28 (MSB)------------------- Bit 13 (LSB) (Bits 12-11 are set to 0)
1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 0

The above line codes to 41000 ft.

Note: Negative values are encoded as the two’s complements of positive values and the negative sign is annunciated in the sign/status matrix.

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  • $\begingroup$ Perfect! Thank you very much Gerry! $\endgroup$ – Hari Seldon Oct 24 '17 at 17:56
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    $\begingroup$ @HariSeldon it is important to note that this only works for those labels. Labels 203 and 204 (for equipment IDs 006,038) use 17 bits of data for a range of 131072 ft with a resolution of 1 ft. It is important to know what Equipment ID is transmitting the value, and for what label $\endgroup$ – selectstriker2 Oct 25 '17 at 18:09

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