Schematic of a GM ALDL -> PC converter

[SRavet at bangate.compaq.com]

Markus Strobl <eusmsrt at exu.ericsson.se> Wrote:
| 
| 
| Does anyone have a schematic of a GM late model ALDL to 
| PC converter? By late model I mean the late 80s/90s
| 8192 baud ALDL. I know the Diacom package has such a 
| converter and someone said it was very simple, but
| I have not been able to find one. I'm planning to 
| write a win95 scantool, but need to be able to 
| talk to the PCM. The diacom uses one pin on the
| parallell port to interface instead of the RS232 and
| that would be fine. 
| 
| Markus
| 

The Diacom software uses the parallel port to watch the serial data pin of 
the ALDL.  It implements a UART in software.  It does have timing problems, 
and in fact at one time you couldn't run it on fast computers.  That's 
really the only way to implement a scan tool without any hardware, though, 
since the ALDL signal is an inverted logic level serial stream.  It'd be 
pretty simple to build a little board with an inverting driver so you could 
drive a regular serial port.  You can't program a PC UART to 8192 baud, but 
you can program it to 8228 using a divisor of 14, which is close enough.  
If I ever get the 5.7 running well in my Blazer, that'll be my next 
project.  This'll be my first car w/ALDL.

--steve

Steve Ravet
sravet at bangate.compaq.com
Baby you're a genius when it comes to cooking up some chili sauce...