timer0.c

PIC单片机的定时器使用的demo程序.内附说明.

#include	<pic.h>

/*
 *	Example code for using timer0 on a 17C756
 *	Just sets up a 1 second interrupt and increments a variable
 */

/*
 *	Calculate preload value for one second timer
 */

#define	PERIOD	1000000		// period in uS - one second here
#define	XTAL	4000000		// crystal frequency - 4MHz
#define	ICLK	(XTAL/4)	// crystal is divided by four
#define	SCALE	16		// prescale by 16 - check for overflow!

#define	PRELOAD	PERIOD*ICLK/SCALE/1000000

unsigned long	seconds;	// second count

/* service routine for timer 0 interrupt */

void interrupt
timer0_isr(void) @ 0x10
{
	seconds++;
	TMR0 += -PRELOAD;	// re-load timer

	// no need to clear T0IF - the hardware did it
}

main()
{
	// initialize timer 0; 
	
	T0STA = 0b01000;		// prescale by 16
	T0CS = 1;			// select internal clock
	TMR0 = -PRELOAD;	// preload timer
	T0IE = 1;			// enable timer interrupt
	GLINTD = 0;			// enable global interrupts
	
	for(;;)
		continue;		// let interrupt do its job
}