f_13_3_tmr0_swmeas.c

* Use 10 MHz crystal frequency. * Use Timer0 for ten millisecond looptime. * Blink "Alive" LED e

#include "config.h"
#include "serial.c"
#include "serio.c"
#include "delay.h"

#if defined(__18CXX)
#include "timers.h"  // timers header file defined by MCC18
#endif

#define FOSCQ 29491200
#define PRESCALE 128.0
#define TMR0TIC 1.0/(FOSCQ/4.0)*PRESCALE

unsigned int tmr0_tics, msec;
double pulse_width_float;
unsigned long pulse_width;
volatile unsigned char capture_flag;

#if defined(HI_TECH_C)
void interrupt timer_isr(void)
#endif
#if defined(__18CXX)
#pragma interrupt timer_isr
void timer_isr(void)
#endif
{
  if (INT0IF) {
    if (!INTEDG0) {
      //seen falling edge, start timer1
      TMR0ON = 1; // turn on timer
      INTEDG0 = 1;  // rising edge interrupt
    } else {
      TMR0ON = 0; // turn off timer
#if defined(HI_TECH_C)
      tmr0_tics = TMR0; // read TRM0 as a 16-bit value
#endif
#if defined(__18CXX)
      {
	   union Timers timer;     //Timers union defined in timers.h of MCC18 lib
         timer.bt[0] = TMR0L;  // Copy Timer0 low byte into union
         timer.bt[1] = TMR0H;  // Copy Timer0 high byte into union
		 tmr0_tics = timer.lt;  // copy to 16-bit integer
	  }
#endif

      INT0IE = 0; //disable RB0 Interrupt
      capture_flag = 1;
    }
    INT0IF = 0;
  }
}
      
void main(void){
  serial_init(95,1); // 19200 in HSPLL mode, crystal = 7.3728 MHz
  // init timer0
  T08BIT = 0; // 16-bit mode
  T0CS = 0;   // internal clock
  PSA = 0;   // use prescaler = 128
  T0PS2 = 1;T0PS1 = 1;T0PS0 = 0; // prescaler = 128
  TRISB0= 1; // RB0 is input
  IPEN = 0; PEIE = 1;  GIE = 1;  // enable interrupts 
  pcrlf();printf("(Timer0 version) Ready for button mashing!");pcrlf();
  while(1){
    capture_flag = 0;
    TMR0H = 0; // clear timer0, write low byte last
    TMR0L = 0;
    INTEDG0 = 0; // falling edge
    INT0IF = 0;  INT0IE = 1; //RB0 Interrupt
    while(!capture_flag); // wait for capture
    // compute time in microseconds
    pulse_width_float = TMR0TIC * tmr0_tics * 1.0e6; 
    msec = (unsigned int)(pulse_width_float/1000.0); //milliseconds
    pulse_width = (long)pulse_width_float;
    //printf ("Switch pressed, timer ticks: %u, pwidth: %lu (us)",
    //	    tmr0_tics,pulse_width);   // use with full HITECH compiler or MCC18
    printf ("Switch pressed, timer ticks: %u, pwidth: %u (ms)",
    	    tmr0_tics,msec);   // use with demo compiler
    pcrlf();
  }
}

//for MCC18, place the interrupt vector goto
#if defined(__18CXX)
#if defined(HIGH_INTERRUPT)
#pragma code HighVector=HIGH_INTERRUPT
#else
#pragma code HighVector=0x0008  
#endif
void HighVector (void)
{
    _asm goto timer_isr _endasm
}
#pragma code
#endif