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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:

Exchange
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. – dccharacter 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 :-) – dccharacter 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. – I have no idea what I'm doing 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
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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. – DucatiKiller Feb 20 '16 at 21:57

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