Tony Nixon [sales at picnpoke.com] of ICmicro's says:
Assume PIC runs at 4MHz 1000Hz wanted at 50% duty cycle
These PWM enable steps are taken from the 16F87X data sheet
- 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
- 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 bitsPWM 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 valuemovlw b'01111101' ; set bits 9 - 2 movwf CCPR1L bcf CCP1CON,CCP1X ; set bit 1 bcf CCP1CON,CCP1Y ; set bit 0
- Make the CCP1 pin an output by clearing the TRISC<2> bitbsf STATUS,RP0 movlw b'11111011' andwf TRISC bcf STATUS,RP0
- 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 2movlw b'00000101' ; TMR2 = on, prescale = 1:4 movwf T2CON
- Configure the CCP1 module for PWMmovf 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.
Liew Danny Jiefu says:
how do you use the pwm after setting it up, for example like on the leds? could u write a sample program?
Searching for so long on internet on how to program PWM for 16f877 and finally I found this! Thanks alot Tony. The datasheet should have consider adding your tutorial to it in the furture. Btw...movf CCP1CON,W andlw b'00110000' ; mask all but previously set Duty Cycle bits iorlw b'00001111' ; and enable PWM mode movwf CCP1CONWhat is the rationale behind this? I know it work but how?
|file: /Techref/microchip/16F877/pwm.htm, 5KB, , updated: 2012/10/1 11:36, local time: 2013/5/20 11:00,
|©2013 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://massmind.org/techref/microchip/16F877/pwm.htm"> Setting up a 16F87x for PWM output</A>
|Did you find what you needed?|
Welcome to massmind.org!
Welcome to massmind.org!