???? Multiple PWM , How to set to different frequenies ???

[Mark30504]

Is there a way set ccp1 and ccp2 (PWM) to diffent frequencies ?

Timer_2 seems to adjust both.

thanks


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[fpgeh]

I'm sure you can do a search to find many ways of performing PWM using a timer. Here's a code snipit anyways that uses timer1. It's not as transparent as the PWM peripherals, but it runs automatically without using many resources.




#define TIMER1_OVERFLOW_CNT 65535

static BOOLEAN pinState;

// These need to be initialized
static int16 cyclesPerPeriod; // must be < TIMER1_OVERFLOW_CNT
static int16 cyclesHigh; // must be < cyclesPerPeriod


#INT_TIMER1
timer1_isr() {
// toggle output and reload timer
pinState = !pinState;
if (pinState) {
output_high(PIN_XX);
set_timer1(TIMER1_OVERFLOW_CNT - cyclesHigh);
}
else {
output_low(PIN_XX);
set_timer1(TIMER1_OVERFLOW_CNT - (cyclesPerPeriod -cyclesHigh));
}

}

[Mark30504]

Hello Thanks

I am trying to use the built in PWM fuctions of ccp1 and ccp2

but I would like to run them at different frequencies.

thanks

[fpgeh]

Yes, I understood your question. Unfortunately, as far as I know only CCP1 is capable of generating PWM outputs. Look at the datasheet. I was just giving an example of using a different resource to generate the 2nd PWM output.

[Roger Courtney]

[Neutone]

[Mark]

You can use the Compare modules to toggle the output pins. With a little thought and careful programming, you can output 2 different PWM frequencies that are "psuedo" hardware controlled. The output is controlled by hardware but you manually load the on off times. Is the frequency a multiple of the other? What frequencies are you wanting and duty cycle? Does the duty cycle change? This method is easier to do on the 18F's since you can use timer 1 & 3 to control the CCP module.