In a message dated 11/16/01 6:33:36 AM Pacific Standard Time,
questuk1@HOTMAIL.COM writes:


> Schmitt input problem on 16F628?
>
> NOTE: the PIC VCC is kept at 5V at all times
> --------------------------------------------------------------------
>
> (The circuit I am interfaced to works at 3V)
>
>
>
> I am reading and writing data, using PortA Bit0.
>
> Everything works ok if the input on the PIC is +5V if I drop this to +3V
> the PIC cannot read it.
> If I substitute the PICF628 for PICF84 everything works correctly down to
> 2.5V
>
> I set up the PICF628 comparators to digital input outputs like this,
>
>
> bsf  STATUS,RP0
> bcf  STATUS,RP1
>
> movlw  B'00000001'      ;All OUTPUTS except Bit0
> movwf  TRISA

Here's your problem. From the datasheet, page 27:

RA5 is a Schmitt Trigger input only and has no output drivers.

There was a post on alt.microcontrollers.8-bit with a simliar problem in that
the PIC would act goofy when trying to set RA5 to output.


Regards,

Tim Hamel


>
> movlw  B'00000000'      ;All OUTPUTS
> movwf  TRISB
>
> bcf  STATUS,RP0
> bcf  STATUS,RP1
>
> clrf  PORTA
> clrf  PORTB
>
> movlw  B'00000111'      ;NOTE must be in Page0, All I/O
> movwf  CMCON           ;Pins,Comparators by default
>
>
>
> Any ideas as to whats wrong?
>
>
> Gary
>

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