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I'm a newbie in ARINC-429 standard. How does the receiver identify which data is in BCD format and which is BNR? I understand that labels indicate the message data carried information, but it does not indicate if the data is BCD format or BNR. If my understanding is correct, the BCD or BNR format used is dependent on the equipment ID. And that leads to my next question: how is the equipment ID embedded in the message?

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The receiver has to be programmed. It's important to remember that A429 is a unidirectional hard-wired bus with a single transmitter and multiple receivers. Each connection is physically unique and the reason for all the pin-out diagrams and bus definitions in the ARINC Characteristics.

To help with data integrity and fault detection, each transmitter includes Label 377 on the bus which contains its equipment ID. For each type of equipment, the label assignments and coding are fixed.

So, if you're building an LRU that's receiving GPS data, you would program the port assigned as the GPS#1 Input to verify the equipment code is 00B hex and the find the specific labels your LRU needs (it's likely to be a small subset of all data on the bus). Since you know the source LRU and the Labels you're looking for, you know the individual label coding and can program the receiver to decode the data.

Most avionics companies have developed custom ASICs to act as the A429 UART. It simplifies the design and saves costs.

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    $\begingroup$ The answer is the first statement, but it could be expanded to say: The receiver doesn't know, it has to be programmed. The developer has to look up the standard and program each port to find and decode the labels it needs. $\endgroup$ – Gerry Sep 27 '16 at 14:07
  • $\begingroup$ Thanks, I saw that 00B hex equipment ID for GPS uses the BNR format for various labels ID according to their respective operations in page 15 A429 specs, Table 1. No BCD format for GPS. Cool! $\endgroup$ – five_thunder Sep 28 '16 at 6:38
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Assume that you are reading data from a LRU that LRU is capable is sending different labels You should program such a way that which label is corresponding to what type of decoding should be done. In general this information will be present in the interface communication document. Like label 05 is encoded in BNR Label 06 is encoded in BCD It is predefined. Hope you understand

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