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PROBLEM WITH PWM..

 
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rantt4
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PROBLEM WITH PWM..
PostPosted: Fri Jun 20, 2008 2:15 pm     Reply with quote
hi
i have to blink a led in a pwm mode but my code somehow turn the led on on a pwm but then it remains ON. i need to blink it while pwm. on and off while pwm.
i add my code.
thanx!

Code:
#include <16F690.h>       
#fuses XT,NOWDT,NOPROTECT,put
#use delay(clock=8000000)

int j; // variable to hold 8-bit PWM value

void main() {

setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_1, 124, 1);
set_pwm1_duty(0);

   while(1)
   {
        for (j=0; j<255; j++){
            set_pwm1_duty(j);
            delay_ms(100);
        }
       
        for (j=255; j>0; j--){
            set_pwm1_duty(j);
            delay_ms(100);
        }
   }
}
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Jun 20, 2008 3:01 pm     Reply with quote
Quote:
setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_1, 124, 1);
set_pwm1_duty(0);

while(1)
{
for (j=0; j<255; j++){
set_pwm1_duty(j);
delay_ms(100);
}

for (j=255; j>0; j--){
set_pwm1_duty(j);
delay_ms(100);
}
}
}

You are running the PWM functions in 8-bit mode. In that mode,
if the duty cycle value is equal to, or greater than the Timer period,
then the PWM output will be a constant high level.


To fix your code, change it as shown in bold below:
Quote:
setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_1, 124, 1);
set_pwm1_duty(0);

while(1)
{
for (j=0; j<125; j++){
set_pwm1_duty(j);
delay_ms(100);
}

for (j=124; j>0; j--){
set_pwm1_duty(j);
delay_ms(100);
}
}
}
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