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.
PORTD++; //Increment PORTD value by one
INTCON.INTF = 0; // clear the interrupt flag
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