PWM Pulse Amplitude on 16F877


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  1. #1
    Join Date
    Feb 2005
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    Indiana
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    Default PWM Pulse Amplitude on 16F877

    I'm getting a good looking 50% duty cycle signal from the CCP1 pin but I just noticed that the amplitude is only about 120mv. I've changed freq and PR2 values and still get 120mv out. I checked the scope setup by going across the 5v reg on the development board and got 5v on the scope.
    I was expecting a 3-5v pulse height. This signal will have to go through some Nand Gates and finally to a transitor base which fires mosfets.
    Any thoughts on the 120mv HPWM output.
    Thanks,
    John
    JRudd

  2. #2
    Join Date
    Jul 2003
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    2,358


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    Have you set the appropriate TRIS for that pin to OUTPUT?

    Have you checked that pin is not shorted against anything else (even breadboards can short against adjacent pins), or otherwise loaded too heavilly with your external circuit?

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