led4_scrolling_interupt.c

#include <xc.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>

int count = 0;
volatile int direction = 1;
 // 1 for going right side, -1 for going left side.
int masks[] = { 0b11111000, 0b11110100, 0b11110010, 0b11110001 };

char next_iteration();

ISR(INT4_vect) { direction = 1; }
ISR(INT5_vect) { direction = -1; }

int main(void)
{
	DDRD = 0x0f;
	DDRE = 0x00;
	
	PORTD = next_iteration();
	PORTE = 0xff;
	
	// enable global interrupt
	SREG |= 0b10000000; // <-- required
	EIMSK = 0b00110000; // <-- enable specific port. pin 4, 5
	EICRB = 0b000001010; // <-- active interrupt when low voltage is detected.
	
    while(1)
    {
		PORTD = next_iteration();
		_delay_ms(100);
    }
}

char next_iteration() {
	count += direction;
	
	if (count > 3) count = 0;
	if (count < 0) count = 3;
	
	return masks[count];
}