dis and timming

[Pat Ford]

Hi all:
 does anyone here have details on the way timming is adjusted 
on a dis ignition. 

What i know
 1) dis module sends out a signal, (refference pulse) and gets
   a signal back from the ecu
 2) the ecu drives another line when it takes over timming control
   from the dis module
 3) the dis module drives a line when a certain rmp is exceeded
   (500 RPM?)

 What I'd like to do is make a small controller that I can down load
a timming map to. what does the ecu output to the dis to modify 
the timing. what does the waveform look like..


any help appreciated
--
Pat Ford                           email: pford at qnx.com
QNX Software Systems, Ltd.           WWW: http://www.qnx.com
(613) 591-0931      (voice)         mail: 175 Terrence Matthews          
(613) 591-3579      (fax)                 Kanata, Ontario, Canada K2M 1W8