ledpwm.c - Demonstrates pulse width modulation by controlling the intensity of an LED. The ADC input value on AN0 is used to vary the PWM period.

#include <stdio.h>
#include <pic24_all.h>
#include <dataXfer.h>



#ifndef PWM_PERIOD
#define PWM_PERIOD 20000  // desired period, in us
#endif

void  configTimer2(void) {
  T2CON = T2_OFF | T2_IDLE_CON | T2_GATE_OFF
          | T2_32BIT_MODE_OFF
          | T2_SOURCE_INT
          | T2_PS_1_64;
  PR2 = usToU16Ticks(PWM_PERIOD, getTimerPrescale(T2CONbits)) - 1;
  TMR2  = 0;       //clear timer2 value
  _T2IF = 0;
  _T2IP = 1;
  _T2IE = 1;    //enable the Timer2 interrupt
}


void configOutputCompare1(void) {
  T2CONbits.TON = 0;          //disable Timer when configuring Output compare
  CONFIG_OC1_TO_RP(RB4_RP);   //map OC1 to RB4
  OC1RS = 0;  //clear both registers
  OC1R = 0;
#ifdef OC1CON1
//turn on the compare toggle mode using Timer2
  OC1CON1 = OC_TIMER2_SRC |     //Timer2 source
            OC_PWM_CENTER_ALIGN;  //PWM
  OC1CON2 = OC_SYNCSEL_TIMER2;   //synchronize to timer2
#else
//older families, this PWM mode is compatible with center-aligned, OC1R=0
//as writes to OC1RS sets the pulse widith.
  OC1CON = OC_TIMER2_SRC |     //Timer2 source
           OC_PWM_FAULT_PIN_DISABLE;  //PWM, no fault detection
#endif
}

void _ISR _T2Interrupt(void) {
  uint32_t u32_temp;
  _T2IF = 0;    //clear the timer interrupt bit
  //update the PWM duty cycle from the ADC value
  u32_temp = ADC1BUF0;  //use 32-bit value for range
  //compute new pulse width that is 0 to 99% of PR2

pulse width (PR2) * ADC/1024

  u32_temp = (u32_temp * (PR2))>> 10 ;  // >>10 is same as divide/1024
  OC1RS = u32_temp;  //update pulse width value
  SET_SAMP_BIT_ADC1();      //start sampling and conversion
}


int main(void) {
  uint32_t u32_pw;
 

Initialize

  configBasic(HELLO_MSG);

Configure PWM

  configTimer2();
  configOutputCompare1();
  CONFIG_RA0_AS_ANALOG();
  configADC1_ManualCH0(RA0_AN, 31, 0);
  SET_SAMP_BIT_ADC1();      //start sampling and conversion
  T2CONbits.TON = 1;       //turn on Timer2 to start PWM

Report results only

  while (1) {
    u32_pw = ticksToUs(OC1RS, getTimerPrescale(T2CONbits));
    printf("PWM PW (us): %ld \n", u32_pw);
    DELAY_MS(100);
    doHeartbeat();
  }
}