GM 2.8L V6 ALDL

[Shawn R. Lin]

Scot Sealander wrote:
> 
> "Shawn R. Lin" wrote:
> 
> > Maybe the checksum calculated by Carbytes 2.0 is wrong, and that's the
> > problem?
> 
> Sounds like it.

Actually, I found out Carbytes is calculating the checksums correctly,
but is changing the string!

> > When I tried sending $F0,$58,$01, it automatically calculated the
> > checksum as $B9.
> 
> Nope.  Should be $B7.  No wonder it ignored the request.
> 
> > If I try sending $F0,$58,$01,$CS, it changes the string to
> > $F0,$57,$01,$00,$B8.
> 
> Whoops, that should be F0 58 01 B7.  The addition of all those bytes
> should add up to zero.  The "CS" stood for Check Sum.

Hahah, DUH!  I feel like an idiot, obviously "S" isn't a hexadecimal
digit!
The problem now seems that Carbytes won't send a $58!
CarBytes automatically changes $F0 $58 $01 to $F0 $56 $01 $B9.
What's up with that???

> > What's the formula for manually computing checksums?
> 
> The last byte sent is the 2's complement of the sum of all the previous
> bytes.  That is, if you add all the bytes in the data stream in byte
> format,
> and ignore carrys, the result should be zero.

I see, MOD 255?

Well, I found out something interesting though...
If I repeatedly try to send $F0 $56 $01 $B9, occasionally the DIC will
read "DIAGNOSTIC MODE", but just for a split second.  The first time it
did that, I thought I was seeing things.  I kept sending $F0 $56 $01 $B9
repeatedly, and sometimes it would leave that message on the DIC for up
to 3 seconds or so, but most of the time just for a split second. 
Sending $F0 $55 $BB will also cause it to flash "DIAGNOSTIC MODE".  It
doesn't stay in this mode, and when I go back to check the chatter, it
is back to normal Mode 0 chatter.  It seems like I'm unable to send the
right string at the right time.  Andy Whittaker's Lotus protocol has $F0
$55 $BB in the chatter, and if I read his page right, he says the PC
needs to send F0 55 BB right after it appears in the chatter.  Then
within 5 seconds, F0 56 01 CS needs to be sent.  Since F0 55 BB is
showing up regularly in chatter, perhaps I need to do the same?

I guess I need a new program to play with...
CarChat bombs with a "Parsing Error".
FreeScan doesn't let me send my own data to the ALDL and doesn't let me
define what is coming in.
GCAR - I can't figure it out (no docs came with it), and it doesn't
format the incoming data.

Any other good progs?

Shawn



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