Can't get POT work on P12f675 - Newbie


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  1. #1
    Join Date
    May 2004
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    Talking Was a pretty good question ....

    Quote Originally Posted by berslan View Post
    Come on guys, did I ask such a stupid question that has to be ignored?
    Hi,

    Yes and No ...

    If you had read your Datasheet ...you could have noticed that GP3 is not a pin like the others ...

    BUT, in your favour, you are not to know how "POT" works ...

    So, just remember POT needs the pin to turn from time to time into an OUTPUT ...

    And this is written nowhere in the manual ...

    The Proof :

    Code:
    POTT    movwf   RM1             ; Save bit mask
            call    HIGHT           ; Set pin high to charge cap
            movlw   10              ; Charge cap for 10ms
            call    PAUSE
            movf    RM1, W          ; Get bit mask
            iorwf   INDF, F         ; Set pin to input
            bcf     FSR, 7          ; Point to port
            xorwf   INDF, F         ; Flip bit to low
            clrf    R0              ; Zero counter
            clrf    R0 + 1
    potloop bsf     FSR, 7          ; Point to TRIS
            movf    RM1, W          ; Get bit mask
            xorwf   INDF, F         ; Set pin to output
            CLRWDT?NOP		; Discharge a little (& clear Watchdog timer)
    Alain

    Change pin used ... no other solution ( ... RCTime won't work either )
    Last edited by Acetronics2; - 26th March 2008 at 12:44.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  2. #2
    Join Date
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    Default

    To add to Alain's explanation, GP3/MCLR is an input only. But huh... why using POT while your PIC have an ADC converter? Check in your manual and on this forum for ADCIN.

    Make sure your pot impedance meet the datasheet requirement (<2.2K if my memory serves me well)

    If you're using a Photoresistor, you will need to use a buffer (op-Amp, transistor or else) in between to match the impedance.
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

  3. #3
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    Smile Cant wait to go home now

    Thanks Alain. Now I get it. In fact I already knew that GP3 is input only and without thinking about how pot works, I used GP3 intentionally, since I could not use it as an output if I needed one later. Smart huh?
    And mister_e, I will give a try to ADCIN. And will make sure to use a analog available pin. thanks for the guidance.

  4. #4
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    Default Hours later, at home...

    Just changed the pin, and it works.
    Thanks a lot guys, you are good.

  5. #5
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    Default

    Usually we don't accept anything under "You're the best"... but Just kidding.

    Enjoy!
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

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