GM 2.8L V6 ALDL

[Dig]

> Date: Thu, 14 Sep 2000 23:14:27 -0400
> From: Barry Tisdale <btisdale at cybersol.com>
> Subject: Re: GM 2.8L V6 ALDL
> 
> This thread concerns the 749 ECU, correct?  From
> working w/ the SyTy box,
> the ECU needs to see F0 56 01 B9 in from 2ms to 5ms
> after the F0 55 BB
> 'chatter'.  Getting this timing right is what's
> giving Paul B a hard time
> getting EFIlive to read the 749s consistantly.

To quote a famous person in our Government-
"AH feel yer payne!"

This very same thing is busting my chops on the VB
app I have to talk to the SyTy/Sunbird code in a
'749 -'730. (Also appears to work this way in a TGP)

I use a 500 ms delay from the recpt. of the 0x55 in
the HeartBeat (HB). This works fabulously on the
two Pentium-class machines I have, but trying to run
it on a 486DX100 laptop is a no-go. Timing looks *way*
off on the scope.

I'm using accurate timers (not code loops), so I know
the delay is consistant from machine to machine. I'd
like to be able to not use a timer, though, since our
Mac friends don't have the same timer architecture 
that we do. It would be nice to have something cross
platform.

One thing that's odd about mine (or maybe not) is that
I TX and RX on the same line without disabling the
output, so I usually read the last part of the message
I sent back in the recieved data. I just strip it off
in the ALDL handler routine.

I think the key, somehow, is when is the bus actually
"free" (ie, floating). The scope kinda shows (tough 
to tell on a 60 MHZ analog) a real little duration
of "high" level voltage that's slightly lower in 
voltage than the open time when the scheduler messages
aren't being sent. I think that's what we're all 
hitting that makes it work (when it does).

Maybe we can do something in hardware (ie, the cable)
to fix it? If we had a level detector to let us know
when the bus was floating, and tied it to CTS, the
interrupt could send the message out.

The TTSpowersystems unit is doing it somehow, though,
with relatively ordinary hardware. There must be a
way...

Later,

Dig


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