I am going to describe a type of communication protocol that I've seen used with ARINC 429 and would like to know if there is a proper name and classification for this type of communication... Anyway, I'll try to describe as accurately as possible.

So there is an outgoing stream of communication (like a heart-beat) that an LRU expects to receive. The LRU also expects to receive certain data on that same heart-beat bus... So, you'd have to sort of inject the ARINC word data into the heart-beat stream temporarily to send it to the LRU.

Is there a name for that sort of communication?

I think I've also seen similar protocols with serial communications... Where a data stream (heart-beat) is always being sent, but the pay-load changes when you need to transmit/receive meaningful data.

I am looking for the technical terms to describe this communication process.

  • $\begingroup$ are you asking specifically for ARINC 429 or in general serial communication interfaces? $\endgroup$ Apr 7, 2017 at 21:51
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    $\begingroup$ Is it possible the OP is referring to Williamsburg/Buckhorn protocol in which there is a "Request to Send" and a "Clear to Send" from the respective transmitter/receiver. Once the handshake is made, the data transfer can begin This (page 17) is a slightly better description. I know it's not quite a "heartbeat," but from my experience with standard ARINC 429 at least, the data transmission is continuous. If the data hasn't changed, the same data just gets repeatedly sent... There is no idling as far as I know? $\endgroup$
    – Frank
    Apr 8, 2017 at 7:53
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    $\begingroup$ @mins Yeah, I see what you're saying. I guess I'm just not really clear on what's being asked. I was taking a stab with the W/B protocol as that is a somewhat unique protocol to ARINC 429. It'd help to know what protocol (429, 615, 573, etc...) the OP is referring to? It might be a little easier to make an inference about what they're asking that way. $\endgroup$
    – Frank
    Apr 8, 2017 at 20:10
  • $\begingroup$ I'm assuming the OP is referring to ARINC 429 based on previous questions, hence my edit to the question $\endgroup$ Apr 9, 2017 at 4:10
  • $\begingroup$ @selectstriker2 Yes, I am only referring to ARINC 429. I shouldn't have said the thing about the serial communications as I believe that it confused what I was trying to ask. I was only using that as an example to say that I believe I've seen a similar kind of pattern involving serial communications in the past... and was not asking about serial communications here in my question. Thanks for clearing that up. $\endgroup$
    – Snoop
    Apr 10, 2017 at 12:05

1 Answer 1


ARINC 429 is both an electrical bus standard and a data standard.

The electrical standard defines a unidirectional, one to many (Tx to Rx) serial data bus that is transmitted using bipolar Return to Zero (RtZ). This makes the signal self clocking. If no data is being transmitted, the line stays at 0 VDC (Null) which consequently removes the clock as well.

Since there is only one transmitter on a line, there isn't any "injection" of data onto the bus by another source.

The ARINC 429 Data standard uses the serial bus to transmit packets of information, called labels. These labels are 4 bytes (32 bits) long.

An ARINC 429 receiver is designed to expect a constant stream of labels to update the receiver's internal data within a certain time limit. If a label isn't received within the specified period it is considered stale and is left to the receiving LRU to decide how to handle stale data.


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