PWM (Duty Cyc;e) PIC16F877A to MD22

[isolde]

Hi I was just wondering is ther anyway in C code I can control the duty cycle of this code:

If ((input(PIN_A2) == 0)&& (input(PIN_A3) == 0))
{
output_low(PIN_C0);
delay_us(2000);
output_high(PIN_C0);
delay_us(1500);
output_low(PIN_C0);
}
else if ((input(PIN_A2) == 0) && (input(PIN_A3) == 1))
{
output_low(PIN_C0);
delay_us(2000);
output_high(PIN_C0);
delay_us(1000);
output_low(PIN_C0);
}

This code acts as a PWM signal and sends the signals I need out. If anyone code give me a idea how to drop the duty cyle by 50% it would be appreciated the signals travels from 0-5V.

 

[Wayfarer]

From your code, If pins A2 and A3 are 00, then C0 will be low for 2 ms and high for 1.5 ms. This gives a duty cycle of 1.5/(2+1.5) = 42.8%

If A2, A3 are 01, then you have C0 low for 2 ms and high for 1 ms giving you a duty cycle of 1/3 = 33.33%

If you want 50% duty cycle, just change the delay time to be equal for low and high.

 

[isolde]

Thanks this helps me alot

 

[andre_luis]

isolde,


Due PIC16F877 already have a built-in PWM hardware module, why don´t you use this ?
There are many advantages comparing with the above code.


+++

 

[samson A.]

Yo seem to be using CSS. why not enter
setup_ccp1(CCP_PWM)
setup_timer_2(T2_DIV_1, PERIOD-1, 15);// prescaler by 1 period of 256 -- ccp freqency = XTAL / (4*PEIOID)
setu_pwm1_duty((long)x); // x = 0 - ((256*4)-1)

or you can say

#define PERIOD 256
#define SetVoltage(x) setup_pwm1_duty((long)(x*(PERIOD*4-1))/ 5)

void main(void){
set_tris_c(0);
setup_ccp1(CCP_PWM)
setup_timer_2(T2_DIV_1, PERIOD-1, 15);// prescaler by 1 period of 256 -- PWM freqency = XTAL / (4*PEIOID)
SetVoltage(2.5); // set for 2.5V

 

[isolde]

Thanks for all the help worked perfect.