I don't see where you're clearing ANSEL.  It powers up as all 1s. making=20
all pins that are analog capable into analog inputs.

Kerry



Clint Sharp wrote:
> I've written a program for a 16F88 that is meant to control an RC servo=20
> with pulses in the range 1.0-2.0 mS. I simulated with MPSIM and=20
> stopwatch, it gives consistent and accurate timings, programming a chip=20
> gives the same results verified with a 'scope and PICKIT2 in logic=20
> analyser mode but as soon as the servo is connected, RB0 pulls high and=20
> stays there.
>
> Changing just the #define in my code to use RA1 (TRISA and TRISB are=20
> cleared) gives me a servo that centres reliably and I can see clean=20
> pulses with the 'scope.
>
> My question, what's different about RA0 and RB0, is it a code issue or=20
> an electrical issue? If I've made a simple mistake or oversight please=20
> put me right, I think I've gone code blind..
>
> I've copied my init sub below, TRISA,0 is set in later code for ADC use=20
> but other than that nothing writes to the TRIS registers once the main=20
> loop is entered.
>
> INIT
>            BANKSEL OSCCON
>            MOVLW   0X72               ; 8MHz USE INT RC AS SYS CLK
>            IORWF   OSCCON,F
>            BANKSEL PORTA
>            CLRF    PORTA
>            CLRF    PORTB
>            BANKSEL TRISB
>            CLRF    TRISA
>            CLRF    TRISB
>            BANKSEL PORTA
>            BCF     INTCON,GIE         ; DISABLE INTERRUPTS
>            CLRWDT
>            BANKSEL OPTION_REG         ; ASSIGN PRESCALER TO TIMER 0
>            MOVLW   B'01010000'
>            ANDWF   OPTION_REG,W       ; WE END UP WITH 01010111
>            IORLW   B'00000111'        ; RBPU=3D0,CLKO FOR TIMER0, PS TO=20
> TMR0
>            MOVWF   OPTION_REG         ; 1:256
>            BANKSEL TMR0
>            MOVLW   0X64               ; LOAD TIMER 0 FOR 20MS INTERRUPTS
>            MOVWF   TMR0
>            BCF     INTCON,TMR0IF      ; CLEAR TIMER 0 INTERRUPT FLAG
>            MOVLW   0X04               ; INT CLOCK,1:1,OSC OFF,NO=20
> SYNC,STOPPED
>            MOVWF   T1CON
>            CLRF    PIR1
>            BANKSEL PIE1
>            BSF     PIE1,TMR1IE
>            BANKSEL PORTA
>  =20



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