GM ALDL interface

[Frederic Breitwieser]

>Does this program take the place of messing with constructing the ALDL-PC
>interface that has bounced around from Peter I believe for a while along
>with the Fiero basic code and all that?  Does it work for both 160 and 8xxx

Actually, it does work pretty well.  I think its similar to the infamous
"turbo link" product that the GN folk buy, desire, etc.  Of course this
program just takes and dumps the data, nothing fancy, so I'm not comparing
the two things...

But it is an excellent framework to build your own ALDL downlink... 

I created a single-transister circuit to make the proper voltage
adjustments (12v to 5v), however over the next day or to I'll have an
opto-isolator circuit that's even better.  Okay, four parts instead of
three, with a wild ballpark in cost of about $8.

>baud ECMs?  Also, what do you mean by you "slowed down" the program?

It just works with the 160 PWM ALDL stuff that GM pumped out in the 80;s.
The 8192 serial data can be read with your PC serial port either directly,
or with a simple UART circuit to do the serial conversion.  Timing requires
effort, but its not a big deal I don't think, though I have a 160 bps PWM
ECM, so I'm focusing on that.

As far as slowing down the program, or speeding it up, the timing loop is
based on "for x=1 to delay / next x" type of software delays to capture
data at the right speed.  The only issue with this the delay loops before
the next byte fetch will vary depending of you have a 286 running DOS only,
or a Pentium 166 running NT with all the multi-media crap installed.  What
I'd ideally like to do is take the efforts Sean started, and work with him
making a windows based ALDL reader software for Win31, 95 and NT, so its
more universal as far as PC requirements.  Interrupt based of course.  Just
that its been ages since I've written a line of code!

Anyway, the basic program that Sean has on his website does work, and I got
a lot of codes out of my 1986 LeSabre ECM that's sitting on the garage
floor.  Lots of codes.  It failed almost all the sensors, but I didn't have
the engine attached to the harness at the time :)

>I just went out yesterday and bought all the parts to build the interface
too!

I did as well, they've been sitting in the box with the packing slip in my
garage, complete with the Maxim chip.  While there is nothing wrong with a
complex circuit that converts to a serial port, this solution is just more
software based.  There's merit for both actually.

I prefer the software method only because I can shove the teeny-tiny
interface into the cable end rather than having a box hanging off the
notebook.  Who knows, maybe I'll start a business making opto-isolated ALDL
cables.  NOT!!!


Frederic Breitwieser
Homebrew Automotive Mailing List
Bridgeport, CT 06606
http://www.geocities.com/MotorCity/Downs/4605/index.html
(Portable Webserver Link Address)

1989 AG Hummer 4-Door
1993 Supercharged Lincoln Continental
2000 Mid-Engine Sports Car <smile>

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