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PWM low frequencies not working

 
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PWM low frequencies not working
PostPosted: Sat Aug 22, 2009 11:12 am     Reply with quote
Hello, Hoping someone can tell that I am doing some stupid here. I can not figure out why i can't get a 20 hz PWM to work. I am using the following code and compiler 4.083.

I am using the following calaulation for the PR2:
//16*16*(193+1)*4/4e6 = period = .049 (s)
//f = 20.4 hz

The code is not giving a 20 hz output. Any ideas on what I'm doing wrong?




Code:

#include <18F4520.h>
#fuses INTRC,NOPROTECT,MCLR,NOBROWNOUT,BORV45,NOWDT,WDT128,NOPUT,NOSTVREN,NODEBUG
#fuses NOLVP,NOWRT,NOCPB,NOWRTB,NOWRTC,NOCPD,NOWRTD,NOEBTR,NOEBTRB
#fuses NOXINST    //extended cpu
#fuses CCP2B3  //multiplex ccp2 to rb3
#use delay(clock=4000000)


#include <lcd_picdem2_2.c>

//ccp2 to rb3 ccp2mx : multiplex ccp2 to rb3: use fuse

//*********************************************************************
void main(){
int8 i = 0, j = 0;

lcd_init();
set_tris_b(0x00);
set_tris_c(0x00);


//tested
/*
setup_ccp1(CCP_PWM);
setup_ccp2(CCP_PWM);
setup_timer_2(T2_DIV_BY_1,32,1);//32.25 khz to get 7 bits resolution for duty cycle//see equeation
*/


setup_ccp1(CCP_PWM);
//16*16*(193+1)*4/4e6 = period = .049
//f = 20.4 hz
setup_timer_2(T2_DIV_BY_16,194, 16);

while(1){



}//while
}//main
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Aug 22, 2009 11:31 am     Reply with quote
The PWM frequency formula is in this thread and in the PIC data sheet:
http://www.ccsinfo.com/forum/viewtopic.php?t=17993

If you still have a problem, then tell us your overall purpose and why
you need a PWM frequency of 20 Hz.
Guest
PostPosted: Sat Aug 22, 2009 5:35 pm     Reply with quote
Ahhhh, postscaler confusion.

The purpose is just for fun stuff. Blinking some led arrays (visibly). Wanted to have some routines that required minimal software control. I see Ttelmah and you have pointed out some good methods in the linked posts. I will implement some of them.

Thanks for the amazing support, as always.
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