Question

Referring to the PCICR and PCMSK registers of the ATMega328P microcontroller, write a fragment of code in C to write to the PCICR and the correct PCIMSK register of the ATMega328P microcontroller to set it up for the following operation:

Pin Changes on Port D Bit 3 or on Port B bit 4 cause a Pin Change Interrupt request.

You may also assume the existence of the macro sei(); to enable global interrupts. Include this in your program fragment in the correct place. There should be three lines in your code fragment.

You can find details of the PCICR, PCMSK0, PCMSK1 and PCMSK2 registers in the ATMega328P datasheet.

Answer 1

#include <conio.h>
#include <stdio.h>
#include <stdint.h> // has to be added to use uint8_t

#include <avr/interrupt.h> // Needed to use interrupts

volatile uint8_t portbhistory = 0xFF; // default is high because the pull-up

void sei(){
  
}

int main()
{
   int DDRB,DDB0,DDB1,DDB2,PORTB,PORTB0,PORTB1,PORTB2,PCICR,PCIE0,PCMSK0,PCINT0;
DDRB &= ~((1 << DDB0) | (1 << DDB1) | (1 << DDB2)); // Clear the PB0, PB1, PB2 pin
// PB0,PB1,PB2 (PCINT0, PCINT1, PCINT2 pin) are now inputs

PORTB |= ((1 << PORTB0) | (1 << PORTB1) | (1 << PORTB2)); // turn On the Pull-up
// PB0, PB1 and PB2 are now inputs with pull-up enabled
  
PCICR |= (1 << PCIE0); // set PCIE0 to enable PCMSK0 scan
PCMSK0 |= (1 << PCINT0); // set PCINT0 to trigger an interrupt on state change

sei(); // turn on interrupts

while(1)
{
/*main program loop here */
}
}

ISR (PCINT0_vect)
{
uint8_t changedbits;

changedbits = PINB ^ portbhistory;
portbhistory = PINB;

  
if(changedbits & (1 << PINB0))
{
/* PCINT0 changed */
}
  
if(changedbits & (1 << PINB1))
{
/* PCINT1 changed */
}

if(changedbits & (1 << PINB2))
{
/* PCINT2 changed */
}

}

--Bold lines are the comments in the program.