Looking for OBD-I link specs for '92 Olds Eighty Eight...

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I post here because googling this only returns a crapload of programmers and devices I have no interest in. (Amazing how suddenly Google went from a search engine to a publicity engine...)

I am wondering if any of you in your automotive electronics adventures ever came by a spec for the OBD-I protocol (at least I am pretty sure those years were OBD-I) used by the ECU in those GM's, as well as anything on the connector's pinout. I have a service manual buried somewhere, but my guess is the information I am looking for relative to the protocol itself will not be in there.

Any help or links would be greatly appreciated... ;)

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I found a history on OBD:
http://www.virtualmechanix.co.uk...

Every specification I found was OBD-II.

This page has some information on reading OBD-I at the bottom.
http://www1.autozone.com/az/cds/...

If you ever move up to ODB-II J1850 protocol, here are some TI reference documents:
http://focus.tij.co.jp/jp/lit/ug...
http://focus.ti.com.cn/cn/lit/ug...

It appears ODB-I is way simpler than ODB-II.

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Shameless self promotion:

http://www.circuitcellar.com/avr...

See also:
http://www.diy-efi.org/gmecm/ecm... ("ALDL data stream formats")
http://en.wikipedia.org/wiki/ALDL
http://www.akmcables.com/aldlif.jpg

The keyword you need for searches is ALDL.

Hope that gets you started. What exactly are you planning to do? Also, curious where in the world you are from (I assume US)?

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Very nice Chris, this is exactly what I was looking for!

I need a simple way to monitor some sensors while doing some tests with H2/O2 supplementing... ;)

I am in Canada.

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Ok so from reading this real quick and seeing the sch for the ALDL to 232 cable, that M pin is just a high impedance data pin, carrying async data at 8192bps for both directions? Seems easy enough to interface, parsing the stream will be something else though, those .txt's are pretty cryptic... ;)

Thanks a bunch, I should be good to go with this...

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The first thing to do is see if your ECU/PCM is 160 baud or 8192 baud. Hope that it is 8192 baud, because 160 is terribly slow and not very useful.

The M pin has a pull-up resistor to 5V internal to the ECU (PCM, computer...) of the car. This acts sort of like a NOR gate, where anything on the bus sees 0V if any single transmitter on the bus pulls it low. Only one transceiver can have control of the bus at a time (half duplex). That also means you receive an echo of what you are sending as you send it.
http://en.wikipedia.org/wiki/Fil...

Also, my Circuit Cellar project was for an ECU/PCM that constantly transmitted data (heartbeat or chatter), but yours probably doesn't have that annoyance and should be much easier to talk to.

Maybe you already know this, but if you need to look at the oxygen sensor(s), they only give you a narrow window of mixture information, but that is another topic... (see: Wideband Oxygen Sensor)

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Curious, Chris - in that competition, there was your OBDI scanner, Trampas Stern's OBDII scanner, and my Bosch/Weber pre-OBD scanner.

Great minds, and all that...

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Yup my datastream is A112 as far as I can see, L27 engine, 3.8L 1992, so it looks like 8192bps... I will just join RX and TX from the AVR's UART and strip echo.

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Neil,
I did find it funny that there were so many car ECU projects. We probably shot each other in the feet for a chance to win. On the other hand, I felt like I kludged it all together and don't even deserve to be on the same page as you two. In any case, it was a lot of fun and I'm glad I was able to get it to work and submit it. Too bad they don't have more AVR contests (not that I need another project).

UNiX,
That sounds like a good plan. Keep us posted on your progress.