Interrupt of PIC 16F877A

Features of the external interrupt that we will use.
The interrupt is triggered by an input on RB0, either ( depending on how we set it up ) as the signal goes from 0 to 1, called the rising edge, or as the signal goes from 1 to 0, called the falling edge. This sets the interrupt flag, and if the interrupt is enabled ( and we are not already in an interrupt ) the microcontroller goes to the interrupt subroutine.
The use of the RB0/Int to manage interrupt externally generated requires the setting of a couple of registers of the picmicro: INTCON and OPTION_REG   

 

It should be clear that the use of RB0/Int function of a picmicro requires the setting of the:
GIE(7): set to 1 to enable global interrupts
INTE(4): set to 1 to enable interrupts on pin RB0
PEIE(6): to disable other periferal interrupts
and the set of the INTEDG bit(6) of the OPTION_REGregister simply to select the  rising or falling edge, of the signal.

When switch is pressed RB0 goes from 0 to 1 causing an interrupt which calls the interrupt() routine. The interrupt routine increment the value of PORD by one. 

Code

  void interrupt(void)

{

  PORTD++;          //Increment PORTD value by one

  //delay_ms(500);

  INTCON.INTF = 0;          // clear the interrupt flag

}

void main(void)

{

  TRISB = 0x01;

  TRISD = 0x00;

  INTCON.GIE = 1;                  //Enable Global Interrupt

  INTCON.INTE = 1;                //Enable RB0/INT external Interrupt

  INTCON.PEIE = 0;                //Disable all unmasked peripheral interrupt

  OPTION_REG.INTEDG = 1;    //Interrupt on rising edge

  PORTD=0;

do

  {

   } while(1);

}

Circuit

Interrupt of PIC 16F877A