Yes Lance you are correct. I had it set as an output.  Actually, the program
starts out and sets PortB<7> as an input but after it goes through the
interupt routine then it changes it to an output. So it is working
correctly.  I had to set the Oscilliscope to a trigger on single in order to
see the 0 to 5v transition during the input stage.

Originally, I did not see this and thought that was why the device was not
working properly,  however, I will need to continue on with the
investigation.  Thanks for getting me past that point.

John

Lance Allen wrote:

> John Wrote..
>
> > I have a PWM input to a PIC16c84 chip.  When I look at the PWM signal
> > from the device, not connected to PIC, it has a nice 0 to 5V signal.
> > When I connect to PIC it has a 4.5 to 5V signal. This causes a problem
> > because the pic always recognizes it as a high signal.  I am guessing
> > that the inherent capacitance on the input to the chip does not have
> > enough time to fully discharge.
> >
> > Does anyone know or can direct me to a source to solve this problem
> >
> I would doubt that input capacitance has anything to do this
> observed result. I would suspect a poor or no common 0volts
> connection between the two devices. That or the PIC pin is
> configured as an output.
>
> If all else fails try a suitable pull down resistor , this will depend on
> the output capacity of the driving device but 10K is a good place to
> start.
>
> _____________________________
>
> Lance Allen
> Technical Officer
> Uni of Auckland
> Psych Dept
> New Zealand
>
> www.psych.auckland.ac.nz
>
> _____________________________