/****** P4_MCC18.c *************************************************************
 *
 * Generate a jitterfree 10 Hz square wave on CCP1 output using compare mode
 * with extension.
 * Use 10 MHz crystal and 2.5 MHz internal clock rate.
 *
 ******* Program hierarchy *****************************************************
 *
 * Mainline
 *   Initial
 *
 * HiPriISR (included just to show structure)
 *
 * LoPriISR
 *   CCP1handler
 *   TMR1handler
 *
 *******************************************************************************
 */
#include <p18cxxx.h>
/*******************************
 * Definitions and equates
 *******************************
 */
#define HalfPeriod  125000      // Number of 0.4 us clock cycles in 0.05 seconds
/*******************************
 * Global variables
 *******************************
 */
char WREG_TEMP;
char STATUS_TEMP;
char TMR1X;                     // Eight-bit extension to TMR1
char CCPR1X;                    // Eight-bit extension to CCPR1
char DTIMEL;                    // Half-period value
char DTIMEH;
char DTIMEX;

/*******************************
 * Function prototypes
 *******************************
 */
void Initial(void);
void CCP1handler(void);
void TMR1handler(void);
void HiPriISR(void);
void LoPriISR(void);

#pragma code highVector=0x08
void atHighVector(void)
{
 _asm GOTO HiPriISR _endasm
}
#pragma code

#pragma code lowVector=0x18
void atLowVector(void)
{
 _asm GOTO LoPriISR _endasm
}
#pragma code

/*******************************
 * main()
 *******************************
 */
void main()
{
     Initial();                 // Initialize everything
     while(1) { }
}
/*******************************
 * Initial()
 *
 * This subroutine performs all initializations of variables and registers.
 *******************************
 */
void Initial()
{
     DTIMEL = HalfPeriod;       // Load DTIME with HalfPeriod
     DTIMEH = (HalfPeriod>>8);
     DTIMEX = (HalfPeriod>>16);
     TRISC = 0b11010000;        // Set I/O for PORTC
     T1CON = 0x81;              // Turn on TMR1
     CCP1CON = 0b00001000;      // Select compare mode
     RCONbits.IPEN = 1;         // Enable priority levels
     IPR1bits.TMR1IP = 0;       // Assign low priority to TMR1 interrupts
     IPR1bits.CCP1IP = 0;       //  and to CCP1 interrupts
     TMR1X = 0;                 // Make first 24-bit compare occur quickly
     CCPR1X = 2;
     PIE1bits.CCP1IE = 1;       // Enable CCP1 interrupts
     PIE1bits.TMR1IE = 1;       // Enable TMR1 interrupts
     INTCONbits.GIEL = 1;       // Enable low-priority interrupts to CPU
     INTCONbits.GIEH = 1;       // Enable all interrupts
}
/****** LoPriISR interrupt service routine ***********************************/
#pragma interrupt HiPriISR      // High-priority interrupt service routine
void HiPriISR(void)             // Included to show form
                                // Supports retfie FAST automatically
{

}

#pragma interruptlow LoPriISR   // Low-priority interrupt service routine
void LoPriISR(void)
{
     while(1)
     {
       if (PIR1bits.CCP1IF)
       {
         CCP1handler();
         continue;
       }
       if (PIR1bits.TMR1IF)
       {
         TMR1handler();
         continue;
       }
          break;
     }

}
void CCP1handler()
{
     if (PIR1bits.TMR1IF)       // If Timer1's overflow flag is set
       if (!(CCPR1H & 0b10000000))  // and compare had occurred after that
         {
           TMR1X++;             // then increment TMR1 extension
           PIR1bits.TMR1IF = 0;  // and clear flag
         }
     if (TMR1X == CCPR1X)       // Check whether extensions are equal
     {
       CCP1CON = CCP1CON ^ 1;   // Toggle control bit (bit 0)
       CCPR1L += DTIMEL;        // and add half period to CCPR1
       if (STATUSbits.C)
         CCPR1H++;
       CCPR1H += DTIMEH;
       if (STATUSbits.C)
         CCPR1X++;
       CCPR1X += DTIMEX;
     }
     PIR1bits.CCP1IF = 0;       // Clear flag
}
void TMR1handler()
{
     TMR1X++;                   // Increment Timer1 extension
     PIR1bits.TMR1IF = 0;       // Clear flag and return to polling routine
}