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,

	Even though I am working on an ALDL project I would be interested in
seeing your code/schematic for the cable use used.  Eventually the next
step for me after getting the ALDL down pat would be to add OBDII
compatibility.  So, yes whatever info you could post would be
appreciated by me and other ECM junkies :)

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