speedo signal specs

[Ludis Langens]

Jeff Bromberger wrote:
> 
> my question is, has anyone scoped this signal?
> i know the pcm puts out 4000 pulses per mile but is it a 0 - 5 volt square
> wave? 0-12V?

Unless you have an oddball configuration, the ECM output is an open
collector driver.  That means it is a switch to ground that opens and
closes.  The circuit receiving the signal is responsible for providing a
pullup resistor to whatever voltage it wants as the logic high level.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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