more ALDL

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

Hi Juz,

I am working on a diacom like tool to release as freeware. So far I have
got a good idea of the interface (connectors, signal level) but have not
yet had success with the protocol. There are some posts in the archive
that explain the checksum and length byte among other things. I know the
byte sequence that is sent (on a '97 Camaro Z) to change direction of
the bus. I just posted that the other day. The rest we need to get from
monitoring a conversation between a Diacom, Xray or Tech tool. We hope
to get data from a tester soon. I am unclear about how different the
years will be.

I don't quite understand your question about both com or lpt versions.
In the case of my ECM, the output is a stream of NRZ data that contains
just a few parameters. It must be commanded (bytes sent to the ECM) to
change pages and provide other parameters. To use the COM port type
interface, you just set the baud rate and shift voltage levels with a
few chips. The LPT or parallel port is a bit more difficult. There the
acknowledge bit can be used to input data. The start bit will cause an
interrupt and a timer is used to determine when to sample each bit. This
bit bash type uart consumes a lot of CPU and other computer resources.
At least one interrupt and one timer. The parallel port must also be
used to shift out bits to the ECM. For that there is a feature in recent
parallel ports that allows two way comms. I havn't decided if I will use
the parallel port or the serial port for my project yet. Both are
possible but the parallel implementation seems like a lot of trouble.

I have a program to change the baud rate on a PC under windows. You can
then use the standard terminal to display data. If you want it just mail
me. That along with the interface (based on the max chip) will allow you
to monitor the data from your aldl port. Not too useful yet but we are
trying.

Tom Hussey

> hi all
> 
> i know that we have all been over the ins and outs of the gm aldl
> interface etc.etc.  and how you can run both COM or LPT versions and i
> have plans for both but has ANYONE got any pland for a DIACOM (type)
> interface????
> 
> "WANTING TO PLAY......MORE"
> 
> Juz!
>