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Newbie PWM problem with PIC 16F627

Started by Deep Reset January 3, 2005
I'm having problems with the PWM module on a PIC 16F627, and I wondered if 
anyone could help please.

The PIC is clocked at 4MHz, and I've got 6 LEDs on port B, including 
RB3/CCP1.

I can write simple light-chaser programs, but I'm trying to dim the LED on 
CCP1, but it is either on, or its off.
My program looks like this:

RESET  MOVLW    B'00000111' ;Disable Comparator modules
              MOVWF    CMCON

              BSF             STATUS,RP0 ;Switch to bank 1

     ;Disable pull-ups
     ;INT on rising edge
     ;TMR0 to CLKOUT
     ;TMR0 Incr low2high trans.
     ;Prescaler assign to Timer0
     ;Prescaler rate is 1:256
             MOVLW      B'11010111' ;Set PIC options
             MOVWF      OPTION_REG ;Write the OPTION register.

             CLRF            INTCON  ;Disable interrupts
             MOVLW      B'11000000' ;RB7 & RB6 are inputs.
             MOVWF      TRISB  ;RB5...RB0 are outputs.

             MOVLW      0xFF  ; all RA are inputs
             MOVWF      TRISA

             MOVLW      100  ; set period for PWM
             MOVWF      PR2

             BCF              STATUS,RP0 ; Switch Back to Bank 0

             MOVLW      5              ; set duty cycle (very low)
             MOVWF      CCPR1L

             CLRF            T2CON  ; Reset prescale and postscale to 1:1

             MOVLW       B'00001100' ; Set PWM mode
             MOVWF       CCP1CON

             BSF                T2CON,TMR2ON ; enable TMR2

LOOP  GOTO LOOP

Just lights the LED on RB3

Any thoughts anyone please?

-- 
Deep Reset 


Dear Deepy,

Deep Reset wrote:

> I'm having problems with the PWM module on a PIC 16F627, and I wondered if > anyone could help please. > > [ sample code snipped ]
>
> Any thoughts anyone please?
Since the PWM module relys on timer 2, you should also turn that timer on (TMR2ON in T2CON). HTH Wolfgang -- From-address is Spam trap Use: wolfgang (dot) mahringer (at) sbg (dot) at
Wolfgang Mahringer wrote:
> Dear Deepy, > > Deep Reset wrote: > > > I'm having problems with the PWM module on a PIC 16F627, and I
wondered if
> > anyone could help please. > > > > [ sample code snipped ] > > > > Any thoughts anyone please? > > Since the PWM module relys on timer 2, > you should also turn that timer on (TMR2ON in T2CON). > > HTH > Wolfgang > > > -- > From-address is Spam trap > Use: wolfgang (dot) mahringer (at) sbg (dot) at
Thanks for the reply, but that is what (I think) the "BSF T2CON,TMR2ON" just before the final loop is supposed to do. I'm pretty sure I checked all the bit assignments. I think I need to borrow a scope, though I'm pretty sure the LED is not PWM'ing - I lit the adjacent LED, and the brightness looks the same. Does anyone know if the PIC simulators allow inspection of the timer registers? I'm not using one at the moment, just taking a suck-it-and-see approach by blowing the code to the controller after each code change. TIA Deep.