[Gmecm] 8192 ALDL bit bang info?

[Danny Sauer]

Jay wrote regarding 'Re: [Gmecm] 8192 ALDL bit bang info?' on Sat, Feb
11 at 19:02:
> Hi there!
> 
> http://www.techedge.com.au/vehicle/aldl8192/8192baud.htm
> 
> Has information on the 8192 bps interface.  Nothing odd here --
> standard RS232 stuff.

So it's a standard RS-232-ish stream?  Well, that's easy enough to
deal with...

http://www.piclist.com/techref/microchip/12F683-rs232-9600-mm.htm

> Considering how electrically noisy an automotive environment is, I'd
> think the checksum going both ways is a good idea.
> 
> http://www.andywhittaker.com/ecu/aldl.htm
> 
> has information on the checksum, but it looks to be checksum  = 0xFF
> - (sum of bytes).  Stated another way, checksum + (sum of bytes) ==
> 0.

Yes, checksums are definitely a good idea.  I prefer to work in as
small of steps as possible, though, and adding 1) software RS232 plus
2) an unfamiliar command set as well as 3) an untested method of
calculating checksums is really a fairly large chunk of code to bite
off all at once - esp. since I'm already using interrupt-driven code.
But that looks like it'll be pretty easy to calculate - just keep a
running sum ignoring carries and then subtract from 255.  Cool.

Thanks much.  I'll put the code up for public consumption once it's
working. :)

--Danny, posting with the *right* address this time :(