GM ALDL codes & questions

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

Hi

I have had several responses from the list, so here is some additional
info. I have had some time off work and spent part of it trying to
figure out the ALDL. As of yet I haven't looked at the OBDII/J1850
stuff. I had some success in this but now I am stuck -and your help
would be appreciated. So here goes...

The input on pin 6 described in an earlier post is a diagnostic mode
input. It looks like this input behaves like some of the earlier ECMs.
There seems to be a "10K" mode, a "3.8K" mode and a shunt to ground mode
(see the archives for more).

I put the scope on the data output and the frames have this wave shape
when a 10K pull down to ground is applied. Here is the wave form...
           __________
          |          |
----------| NRZ DATA |--------------------
          |__________|

~30ms     |  ~20ms   |    ~30ms

During the data phase the data line on pin 2 is driven both high and
low. This differs from some info in the archive for earlier controllers
that suggest the line is open collector/drain. If the line is
bi-directional (I think so), the gap between frames would be used to
send data/instructions to the ECM. I think this would be used to select
the parameter set to return. 

I have decoded some of the data sent by the ECM, but there is not near
enough sent to hold all the parameters. Thus I think that an
"instruction" needs to be sent during the inter frame gap to request a
different parameter set. If these instructions are to be sent, only
disassembly of the ECM code would give us the format & codes needed. 


Now I am stuck and asking for your help.

- Does anyone know how to get the ECM to send different parameter sets?
- Does anyone have access to ANY eprom/eeprom from an ECM that uses the 
8192 baud format?
- Any ideas on how to get the ecm to dump out its data?


Thanks for your help -Tom Hussey





> 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 
> > 
--snip--
> > 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
> 
---snip