interrupt

]#include   <pic.h>

/*
 *   Interrupt demo for PIC; wait for button press on RB0/INT,
 *   turn on a relay on another port bit for a period of time.
 *   For simplicity here, literal constants are used, usually these
 *   should be calculated with compile-time arithmetic.
 */

#define RELAY RB4                             // use this bit to drive relay

static unsigned int   relay_timer;         // timer value for relay driver

           void main(void)
{
                  /* setup stuff */

             RELAY = 1;                             // ensure relay is off before enabling output
             TRISB = 0x03;                       // Port B bits 7 and 6 are output 

              OPTION   = 0b00000111;
              TRISB   = 0b00000011;

               RBPU = 0;                           // Use internal pullups
               T0IE = 1;                            // Enable interrupt on TMR0 overflow
               INTEDG = 1;                      // falling edge trigger the interrupt
               INTE = 1;                          // enable the external interrupt
               GIE = 1;                            // Global interrupt enable
               for(;;)
   {
               CLRWDT();                       // Idly kick the dog
   }
   }

                static void interrupt
  
                isr(void)                                .
{
                if(T0IF)
{                                                            // timer interrupt
                PORTB ^= 4;
                if(relay_timer)
{                                                                 // is the relay timer running?
               relay_timer--;                                      // decrement it
               PORTB |= 8;
 }
            else
{
             RELAY = 1;                // turn the relay off
             PORTB &= ~8;           // toggle a bit to say we're alive
 }
            T0IF = 0;                     // clear the interrupt flag
  }
            if(INTF) 
{                                             // did we see a button press?
            RELAY = 0;                   // turn the relay on
            relay_timer = 16;           // start the timer - 16 timeouts ~ 1 second
            INTF = 0;                       // clear the interrupt
   }
}