A typical connection used to transmit/receive ARINC data might consist of a cable and a connector similar to the one shown below. Although ARINC transmit/receive channels aren't the only thing this interface can be used for. I've noticed that several different varieties of LRU also use some of the pin connections for I/O discretes.

A typical connector used for ARINC signals.

So, are the I/O discretes considered to be part of the ARINC interface? Or do they just coincidentally share the same connector and have nothing to do with ARINC?


As one of the answers commented on... I am not talking about the discrete bits within an ARINC word but the physical discrete I/O voltage signals that you'd see on an avionics bus.

  • $\begingroup$ With ARINC 429 being a single transmit/multiple receiver bus, that connector probably has 4 A429 transmit (8 pins), 8 A429 receive (16 pins) and 6 discretes (6 pins). I've dealt with multiple 100 pin connectors where 2/3 were A429. $\endgroup$ – Gerry Apr 13 '17 at 23:33
  • $\begingroup$ These Mil Std connectors are used on most LRUs for reasons stemming from DO-160. ARINC 429 data lines get passed as one of the many pins on the connector. The other pins may be discrete, analog, or digital signals for different inputs or outputs that aren't even related to ARINC 429. $\endgroup$ – selectstriker2 Apr 14 '17 at 13:39
  • $\begingroup$ @selectstriker2 The majority of avionics are ARINC 700 series (what Boeing and Airbus use) and don't use MIL-STD connectors. They use ARINC 600 blind mate connectors - they're on the rear of the units and mate when the LRU is slides into the mounting tray. They are 'locked' when the LRU is locked into the tray. Boeing and Airbus do use the MIL-STD connectors in the wiring harnesses at bulkheads,etc. There are some non-ARINC 600 LRUs typically outside the EE Bay where they do use MIL-STD connectors as they don't want the added weight of the racking system. $\endgroup$ – Gerry Apr 17 '17 at 14:29
  • $\begingroup$ @Gerry Once again... Was asking about ARINC in general, but ARINC-429 tag was the closest I could get. $\endgroup$ – Snoop Apr 17 '17 at 14:38
  • $\begingroup$ @Snoopy Agreed. I was commenting on selectstriker2's comment about the use of MIL-STD connectors. He said they were used on most LRUs. I pointed out that the majority of ARINC LRUs use the ARINC 600 connectors. MIL-STD connectors are used in the harnesses and in some remote LRUs, but I wouldn't say they are used in the majority. $\endgroup$ – Gerry Apr 17 '17 at 14:47

It depends on which ARINC document you're talking about. ARINC 429 is a digital serial bus standard. Discrete data may be sent in ARINC 429 data words, but that's just bits in a word not the physical discretes you're asking about.

ARINC also has documents that cover standards for other interfaces as well as 'Characteristics' that define specific LRUs such as ARINC 735A for TCAS II. In these documents ARINC does specify discrete interfaces. There are two types, open/ground and 28V/open and are defined for both input and output.

So yes, there are discrete interfaces that are part of ARINC standards, just not part of ARINC 429.

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  • $\begingroup$ Yeah... So what I wanted to do for this question was ask about ARINC in general, i.e. 429/600/717. However, because my reputation is too low I had to pick the 429 tag because it is the closest thing. Really I would like to be able to use a generic ARINC tag for this. $\endgroup$ – Snoop Apr 13 '17 at 13:06
  • $\begingroup$ Also, thanks for pointing out that I'm talking about the physical discretes. That is exactly what I meant. It's good you were able to pick that out but I may still need to update my question to clarify a bit further. $\endgroup$ – Snoop Apr 13 '17 at 13:07
  • $\begingroup$ One thing to note, ARINC is a standards and services company owned by Rockwell Collins. So a generic ARINC tag wouldn't really be applicable for what you are asking. I do know that we don't follow any sort of defined standard for our discrete I/O's but they do go through DO-160 testing. $\endgroup$ – selectstriker2 Apr 13 '17 at 13:21
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    $\begingroup$ @selectstriker2 While Rockwell-Collins did buy ARINC, it did so to obtain their data link services company. Since R-C is an avionics company, owning the standards committees would be a conflict of interest. As a result, R-C sold the ARINC Industry Activities portion of the company to SAE (Society of Automotive Engineers). So ARINC-IA, the producers of ARINC Standards and Characteristics, is not the same as ARINC. $\endgroup$ – Gerry Apr 13 '17 at 16:31
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    $\begingroup$ @selectstriker2 I don't disagree with your position on the tag. There's only 8 questions with the ARINC-429 tag and no other ARINC type tags. While there are over 100 ARINC standards, I doubt there would be enough questions against them to justify a tag. The Avionics tag works well for these type questions. If there was interest, it might be more appropriate to have a general Industry Standards tag. $\endgroup$ – Gerry Apr 13 '17 at 23:39

This is an old question, but as I've stumbled, others will too, and the comments seem to have deviated a bit. Yes the physical discrete pins are part of ARINC standards, and their electrical specs are defined in subsection 2.2.1 of ARINC 628-1 (newer) and 4.1.4 of ARINC 726 (old) standards. The question is if they're "part of the ARINC interface" - but ARINC standards define a lot of interfaces and systems, and "arinc interface" will not point to one specifically.

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    $\begingroup$ Not all discretes will follow an ARINC standard though, unless they are specifically for equipment conforming to an ARINC standard or using an ARINC defined connector (like the ARINC 600 series connectors @Gerry mentioned) $\endgroup$ – selectstriker2 Mar 7 '19 at 23:04

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