Embedded Projects Blog: Interrupt of PIC 16F877A

Interrupt of PIC 16F877A


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_REG register 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

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