I'm trying to figure out what is the serial protocol that is used in Honda Odyssey 2007 for communication between RES (rear entertainment system) DVD drive and main audio head. I was convinced it would be GA-NET (IEBus), but after failing to use a device to decode that bus, I hooked up a scope and was surprised to see that the wires are not differential but rather RX/TX.

Here's how they talk:

And this is a closeup of what I believe is somewhat like keep alive response from DVD.

Close up

I was really surprised to see this. Baud rate seems to be in between 1200-4800 if my assumption is correct - this lust closeup looks like 3-4 bytes (if this is a 8-bit exchange at all). Or maybe it's LIN and the packet sizes are 11 and 29 bits? I'm very confused, will appreciate help.

Thanks a lot in advance!

Sorry about the markup - I'm totally unable to figure it out. When you read help - it looks really simple, but when you try to actually use it - it's total failure.

  • Have you tried ordinary garden UART? 1200 2400 4800 are all standard UART baud rates?
    – vini_i
    Feb 18 '16 at 2:25
  • Actually no :-) I shall probably do so. Feb 18 '16 at 2:32
  • Nothing human readable comes out. I did tests with both non-inverted (forgot to invert) and inverted (obviously that is correct) with all kind of baud rates, including non-standard like 3000 and 3600 and 6000. This says to me (maybe I'm incorrect) that the exchange is a byte-stream (if it's plain UART at all), not ASCII stream. Or it's in Japanese :-) Feb 18 '16 at 3:15
  • Well, it's very unlikely to be ASCII. Honestly it would be tough to tell without knowing what it is in advance, might be a non-standard protocol. You can write down a few sequences and see if it has a start byte, length byte(s) or CRC byte(s) at the end. Feb 18 '16 at 8:22
  • All protocol that I know of have some kind of start sequence, some ID, a data part and usually a CRC. I THINK that LIN for example has first a "break" with just zeros, and then a sync with 101010101010 and since I can't see anything like that sync I wouldn't think it's LIN. First try to identify a pattern where the message starts and ends, then maybe you could just ignore what the messages looks like, but identify that a message that looks like this is a play_next_key_pressed message etc. Fun project by the way!
    – Markus
    Feb 19 '16 at 11:21

This is 8e1 9600 b/s inverted UART. The second graph represents 6 byte packet.

  • You can award yourself the answer to this. :-) Cheers, welcome to the site. Feb 20 '16 at 21:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.