Diacom cable for GM

[sfg]

swagaero wrote:
> 
> sfg wrote:
> >
> > I purchased the Diacom diagnostic interface (GM) kit back in '92. It
> > runs under DOS and has been worth the $200 or so I spent on it.
> > The supplied cable, which connects your RS232 to the ECU (ALDL) has a
> > red wire for 12VDC input. Recently I discovered the system works with,
> > or without the 12VDC connected. I had always assumed there were active
> > components molded into one of the connectors; now I am wondering if its
> > really just a hunk of wire, with connectors on each end. Anyone know?
> > Steve
> 
> diodes, diodes, diodes, diodes and more of them used as gates and most
> ECM's don't neeed the voltage
> 
> Steve Parkman
> --
> 
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> :http://www.flash.net/~swagaero

Steve, please elaborate a bit. If you are familiar
with this interface cable please, enlighten us. When I first saw the
+12VDC wire, I followed the Diacom instructions to connect it. Later I
found by accident that it wasn't reqd. (initial assumption being that
there was logic-level conversion or inversion going on, or pull-ups
required, and ICs were potted in the connector shell...too much to
expect GM to provide RS232 right at the ALDL) Are all output
pins on the GM ECU open collector? Is there a FAQ on this which I 
missed in the archives (I've looked).
Whats the scoop?  
Steve Gent    "well built 383 SBC seeks hot TBI for fun & torque" .....