#include <at89x51.h>

#define ON 1
#define OFF 0
#define HIGH 1
#define LOW 0

void Timer0_ISR (void) interrupt 1;	// ISR for Timer0 overflow

void Timer0_ISR (void) interrupt 1
{
    if(F0 == LOW) {  /* Just finished the LOW period, switching to HIGH */
        F0 = HIGH;
        P1_0 = OFF;  /* Turning on P1_0 */
        TH0 = 0xFA;  /* Setting timer start value to 64245 */
        TL0 = 0xF5;
        TF0 = 0;     /* Reset Timer Overflow Flag */
    }

    else {           /* Just finished the HIGH period, switching to LOW */
        F0 = LOW ;
        P1_0 = ON;   /* Turning off P1_0 */
        TH0 = 0xC3;  /* Setting initial timer value to 50068  */
        TL0 = 0x94;
        TF0 = 0;     /* Reset Timer Overflow Flag */
    }

    return;
}

void main (void)
{
    EA = ON;       /* Enabling All Interrupts */
    ET0 = ON;      /* Enabling Timer 0 Interrupt */

    TR0 = 0;       /* Stop Timer 0 */
    TF0 = 0;       /* Reset Timer Overflow flag */

    TMOD &= 0xF0;  /* Set Timer 0 to Mode 1 (16-bit no prescalar) */
    TMOD |= 0x01;  /* Set Timer 0 to Mode 1 (16-bit no prescalar) */

    TH0 = 0xC3;    /* Setting initial timer value to 50068 (i.e. LOW period) */
    TL0 = 0x94;

    F0 = HIGH;     /* Setting F0 Flag to HIGH */

    P1_0 = OFF;    /* Turning off P1_0 */

    TR0 = 1;       /* Starting Timer 0 */

    while (1)
    {
    }
}