#define _XTAL_FREQ 20000000                // set crystal oscillator to 20MHz.
#define TMR1PRESCALE 8                     // timer1 prescaler is 8.
#define OUT RC2                            // use the name OUT for RC2 pin.

#include <xc.h>

// BEGIN CONFIG
#pragma config FOSC = HS   // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF  // Watchdog Timer Enable bit (WDT enabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON  // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF   // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3 is digital I/O, HV on MCLR must be used for programming)
#pragma config CPD = OFF   // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF   // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF    // Flash Program Memory Code Protection bit (Code protection off)
//END CONFIG



// variables and constants declarations
unsigned long CCPR = 0;                    // holds the value needed to be put in CCP's registers.
unsigned long current_period = 0;          // holds the period that timer1 will use.
const unsigned long total_period = 12500;  // 20ms for 50hz frequency.


// interrupt service routine
void interrupt tmr1isr () {
   if (CCP1IF == 1) {                           // if CCP compare interrupt flag is set


       if ((current_period > 0) && (current_period < total_period)){ // if duty is > 0% AND < 100% then:

           if (OUT == 1) {                           // if the output was 1 -> was "on-time".
           OUT = 0;                                  // set output to 0 in order to achieve "off-time".
           CCPR = total_period - current_period;     // make it time for "off-time", off-time = full time - on time.
           }

      else {                                    // if the output was 0 -> was "off-time".
         OUT = 1;                               // set output to 1 in order to achieve "on-time"
         CCPR = current_period;                 // make it time for "on-time".
      }
       }
       else {
           if (current_period == total_period) { OUT = 1;}             // if duty = 100%, then output 1 all the time.
           if (current_period == 0)            {OUT = 0;}              // if duty = 0%, then output 0 all the time.
       }


      // now set the value of CCPR into CCP module's registers:

      CCPR1H = CCPR >> 8;                       // right-shift CCPR by 8 then load it into CCPR1H register (load higher byte).
      CCPR1L = CCPR;                            // put the lower byte of CCPR in CCPR1L register.
      CCP1IF = 0;                               // reset CCP1 interrupt flag.
   }
}


// main function:
void main() {


   TRISC = 0;                 // port c is output.
   PORTC = 0;                 // port c = 0.

   T1CON = 0b00110000;        // timer1 uses prescaler value of 8 and it is off.
   TMR1H = 0;                 // timer1 registers have 0 (clear).
   TMR1L = 0;

   CCP1CON = 0x0b;            // set CCP module to compare mode and trigger special event when interrupt happens.
   CCPR = 0;                  // load 0 in CCPR.
   CCP1IF = 0;                // clear CCP1 interrupt flag.
   CCP1IE = 1;                // enable CCP1 interrupt.
   INTCON = 0xC0;             // enable global and peripheral interrupt.
   T1CON = 0b00110001;        // start timer1 with the same settings like before.




   while (1) {                                          // infinite loop.


       // TEST CODE...

       current_period = total_period * 0.5;            // 50% duty cycle.
       __delay_ms(2000);                               // delay 2s.
       current_period = total_period * 0.1;            // 10% duty cycle.
       __delay_ms(2000);                               // delay 2s.
       current_period = total_period * 1;              // 100% duty cycle.
       __delay_ms(2000);                               // delay 2s.
       current_period = total_period * 0;              // 0% duty cycle.
       __delay_ms(2000);                               // delay 2s.
      }
   }