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31st January 2005 04:41 PM #1 
Can anyone explain the difference between VWP & PWM?
whats the difference between Variable width pulse & pulse width modulation?
can you help me explain it or point me in the right direction of a web site that explains it?
thanks
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1st February 2005 02:51 AM #2
VWP has to be defined by whomever made up the term. PWM normally runs at a constant frequency and varies the duty cycle. Some systems have a constant pulse width and vary the frequency, but that would not be VWP. Maybe VWP is constant duty cycle and vary the frequency, not a very sensible thing to do.
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1st February 2005 03:46 AM #3
The datasheet for the 555 oscillator/timer shows a Pulse Position Modulator that changes both the frequency and duty-cycle at the same time. Maybe that is also called Variable Width Pulse.
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2nd February 2005 01:26 AM #4
Are you possibly looking for info on the Ford / GM communications protocols used in their respective OBDII systems. If so, Google OBDII or OBD-2 and see what comes up.
Several sites discuss, some in great detail, the protocols and associated timing/signal types used.
Dialtone
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