ALDL

[sdbartho at cca.rockwell.com]

> > sdbartho at cca.rockwell.com Wrote:
> > | 
> > I don't think there is a way to send commands to the ECM on the ALDL system, 
> > since there is only one data line.  The ECM transmits it's info over the li 
> > the dash listens in for some info it needs.  As far as I know the different 
> > resistances on the A-B line set the different modes.  This applies to the 
> > 8192 baud stream in late model corvettes, others I don't know.

This was Steve's reply to my message, just to clear up some threading con-
fusion.

> That sets the ECM diags mode, the serial data mode can be set independantly
> of the ECM diags mode. Normally they are linked. The 8192 ALDL
> setup indeed uses bidirectional data on the one line.... it's a master-
> slave protocol, with the ECM being the slave, and the diag tool the
> master. They do this by Hi-Z buffers on the line (or by using an open-
> collector output stage, depending on who you talk to).

Ahh, so the ALDL _output_ line is bidirectional? The info I have said that
there was an input/output protocol, but wasn't really clear about which
line was the input. The impression I got was that the Diag input was 
also the ALDL serial input.


Dig
sdbartho at hwking.cca.rockwell.com