GM ALDL codes & questions

[Mark Glicksman]

TOM_HUSSEY at HP-Canada-om1.om.hp.com wrote:
> 
> Hi,
> 
> This is my first post to this list. I own a '97 Camaro Z28 and have an
> interest in learning about the on board computer. To date I have been
> working with the ALDL port to decode the format. I have a single board
> computer based on a 68HC11F1 that has been used for all my efforts. So
> far my understanding is based on the book Computerized engine controls
> 5th ed by Dick King and data sheets from Harris semi.
> 
> I understand this car has an "OBDII" interface. The OBDII interface
> takes up four of the six pins that are used on the connector. I think
> the pinout is:
> 
>    ------------------------------
>     \  1  2  3  4  5  6  7  8  /
>      \ 9 10 11 12 13 14 15 16 /
>       -----------------------
> Pin  2 is the data
> Pin  4 is chassis ground
> Pin  5 is signal ground
> Pin  6 is an input....What for ?  -> Non OBD II pin
> Pin  9 is NRZ serial data         -> Non OBD II pin
> Pin 16 is Battery
> 
> The NRZ serial data link at 8192 baud 8/N/1. I wrote a software UART
> program to look at this interface and got the following types of hex
> codes:
> 
> 91 59 00 00 00 00 16
> 90 5a 25 08 44 44 ff 62 ff
> oa 58 aa 03 92 5f ff
> 
> I know that the "03 92" represents 914 RPM in the last frame. The "44
> 44" in the second frame are suspect to be temperature. Could anyone help
> me with the format decode?
> The second non OBDII signal on the connector is an input on pin 6. Can
> anyone tell me what it is used for?
> 
> I wrote a routine to extract the data from J1850 pwm format. When I went
> to look at the data I found that there is no signal on the pin (pin 2).
> How is the computer prompted to send data to the J1850 I/O pin?
> 
> If anyone would like the code I have written let me know. Any assist on
> the decoding of the data would be great. Thanks -Tom Hussey

Hey Tom,

	I'm not sure If I've replied to this email, but yes I would be
interested in seeing the code you wrote for it.  As for decoding it I'll
see what I can do.

			VTY
			Mark Glicksman
			mglicksm at suffolk.lib.ny.us