GM ALDL codes & questions

[TOM_HUSSEY at HP-Canada-om1.om.hp.com]

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