outputcompare_oneservo.c - Demonstrates servo control using output compare for PWM. Pulse width is set by the ADC input.

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


#ifndef PWM_PERIOD
#define PWM_PERIOD 20000  // desired period, in us
#endif
#define MIN_PW 600   //minimum pulse width, in us
#define MAX_PW 2400  //maximum pulse width, in us

void  configTimer2(void) {
  T2CON = T2_OFF | T2_IDLE_CON | T2_GATE_OFF
          | T2_32BIT_MODE_OFF
          | T2_SOURCE_INT
          | T2_PS_1_64 ;  //1 tick = 1.6 us at FCY=40 MHz
  PR2 = usToU16Ticks(PWM_PERIOD, getTimerPrescale(T2CONbits));
  TMR2  = 0;       //clear timer2 value
  _T2IF = 0;
  _T2IP = 1;
  _T2IE = 1;    //enable the Timer2 interrupt
}

uint16_t u16_minPWTicks;
uint16_t u16_maxPWTicks;

void configOutputCompare1(void) {
  u16_minPWTicks = usToU16Ticks(MIN_PW, getTimerPrescale(T2CONbits));
  u16_maxPWTicks = usToU16Ticks(MAX_PW, getTimerPrescale(T2CONbits));
  T2CONbits.TON = 0;       //disable Timer when configuring Output compare
  CONFIG_RB4_AS_DIG_OUTPUT();
  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 using ADC value

(max - min) * ADC/1024 + min

  u32_temp = ((u32_temp * (u16_maxPWTicks-u16_minPWTicks))>> 10) + u16_minPWTicks;  // >>10 is same as divide/1024
  OC1RS = u32_temp;  //update pulse width value
  AD1CON1bits.SAMP = 1; //start next ADC conversion for next interrupt
}

int main(void) {
  uint32_t u32_pw;
  configBasic(HELLO_MSG);
  configTimer2();
  configOutputCompare1();
  CONFIG_RA0_AS_ANALOG();
  configADC1_ManualCH0(RA0_AN, 31, 0); //this is 10-bit mode
  SET_SAMP_BIT_ADC1();      //start sampling and conversion
  T2CONbits.TON = 1;       //turn on Timer2 to start PWM
  while (1) {
    u32_pw = ticksToUs(OC1RS, getTimerPrescale(T2CONbits));
    printf("PWM PW (us): %ld \n",u32_pw);
    DELAY_MS(100);
  }
}