Aldl Communication

[Andrew Wakeling]

Hi all,
Just if anybody's interested, I've laid my hands on the BUA chip. It was
a while ago, but it was in demand then so e-mail me if you want it and I
can send it to you.

Now, my current problem is very interesting. I have three proms, BUA,
ABTD and AANM all which suit a corvette... either '87 or '86. Anyhow, I
wanted to write my own little program to get the aldl stream because I
wanted to manipulate the data a bit more just to try some things. I know
that the procedure to link to this type of prom is a little wierd. This
is the procedure that I'm going through.

ECM is initially in 160 baud
10k resistor to put prom in ALDL mode
Prom starts to put out a 25 item 160 baud stream
At the end of the stream the ECM listens for 50ms for a 8192 request
Once a request is sent, the ECM stays in 8192 baud and everything is
sweet.

RIGHT, everything seems to work perfectly in Diacom for all three chips,
however when I use my device it only links with ABTD. I've tried
everything possible and I've narrowed things down a little.

I've used Diacom to put all three proms in 8192 baud and after that I
have no problem linking with my device, so that must mean that the
stream requests and reads are a.o.k.

Then I thought, maybe the resistor value was wrong, so instead of
plugging Diacom's resistor lead into the plug, I substituted my
resistor. Diacom worked perfectly, that means that my resistor was also
ok.

I then checked to see if Diacom was sending anything else... I didn't
pick up anything at 8192, except a 0xFF... maybe a falling/raising edge
or something? I think THIS is my problem.

One more thing, that Diacom worked perfectly with all proms also
indicating that my ECM, loom, computer and other stuff was ok.

So, is my presumption correct that Diacom is sending something else? Or
is my device faulty or something? I can't seem to figure this one out...
Too many late nights. If only I could swap get proms to the 8192 polling
mode, then everything would be ok.

One more thing was that I was unsure about the VATs having to be
bypassed. Diacom didn't have a problem, and also that fact that Diacom
doesn't put anything into B6 (VAT pin) means that it should also be ok
to get the stream while VAT is looking for that startup signal.

If anybody could give me any hints to my problem that would be great.

Andrew Wakeling.