Dilan Amarasinghe wrote:
>
> Hi,
>
> Can some one send me the CODE to set the PWM of 16F877 to 10Khz with 50% duty.
>
> Best Regards
>
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I posted this awhile ago. It outputs 1000Hz but you should be able to
figure out how to make it work at 10KHz.




Assume PIC runs at 4MHz
1000Hz wanted at 50% duty cycle

These PWM enable steps are taken from the 16F87X data sheet



1. Set the PWM period (1000Hz = 0.001S) by writing to the PR2 register.

   PWM Period = [PR2 + 1]*4*Tosc*TMR2 PreScale value

   Use 4 for TMR2 prescale. You can try other values but make sure it
   works with the duty cycle calcs as well.
   Tosc = 1/4000000 = 2.5*10-7
   Rearranging the equation gives...

   PR2 = (Period/(4 * Tosc * TMR2 Prescale)) - 1

   Therefore...

   PR2 = (0.001/(4 * 2.5 * 10-7 * 4)) - 1 = 249

   bsf STATUS,RP0
   movlw d'249'    ; when TMR2 = 249 = end of Period
   movwf PR2
   bcf STATUS,RP0

2. Set the PWM Duty Cycle by writing to the CCPR1L register and
   CCP1CON<5:4> bits.

   CCPR1L contains the upper 8 bits of the 10 bit Duty Cycle value
   CCP1CON<5:4> contain the lower 2 bits

   PWM Duty Cycle = (CCPR1L:CCP1CON<5:4>)*Tosc*TMR2 Prescale Value

   CCPR1L:CCP1Con<5:4> = PWM Duty Cycle / (Tosc * TMR2 Prescale)

   PWM Duty Cycle = 50% of Period

   PWM Duty Cycle = 50% of 0.001 = 0.0005

   CCPR1L:CCP1Con<5:4> = 0.0005 / (2.5 * 10-7 * 4)

   CCPR1L:CCP1Con<5:4> = 500

   500 in 10 bit binary = 0111110100

   CCPR1L = 01111101    CCP1Con<5:4> = 00

   Write the 10 bit value

   movlw b'01111101'  ; set bits 9 - 2
   movwf CCPR1L
   bcf CCP1CON,CCP1X  ; set bit 1
   bcf CCP1CON,CCP1Y  ; set bit 0

3. Make the CCP1 pin an output by clearing the TRISC<2> bit

   bsf STATUS,RP0
   movlw b'11111011'
   andwf TRISC
   bcf STATUS,RP0

4. Set The TMR2 prescale value and enable TMR2 by writing to T2CON.

   We decided previously to set the prescale value to 4.

   TMR2 prescale are bits 1 and 0 in T2CON
   TMR2 enable is bit 2

   movlw b'00000101'   ; TMR2 = on, prescale = 1:4
   movwf T2CON

5. Configure the CCP1 module for PWM

   movf CCP1CON,W
   andlw b'00110000'  ; mask all but previously set Duty Cycle bits
   iorlw b'00001111'  ; and enable PWM mode
   movwf CCP1CON

A 1000 Hz square wave with a 50% duty cycle should now be coming out of
RC2.
--
Best regards

Tony

mICro's
http://www.picnpoke.com
mailto:sales@picnpoke.com

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