#include <avr/common.h>
#define F_CPU 4000000UL
#include <util/delay.h>
#include <avr/interrupt.h>

void setColumnToZero(char bit)
{
	bit = 3 - bit;
	PORTA &= ~_BV(bit);
}

void setColumnToOne(char bit)
{
	bit = 3 - bit;
	PORTA |= _BV(bit);
}

char isRowZero(char bit)
{
	bit += 4;
	return (PINA & _BV(bit)) == _BV(bit);
}
  
void timer1_init()
{
    TCCR1B |= (1 << WGM12)|(1 << CS11)|(1 << CS10);
  
    TCNT1 = 0;
  
    OCR1A = 24;
  
    TIMSK |= (1 << OCIE1A);
  
    sei();
}

ISR (TIMER1_COMPA_vect)
{
	for (char i = 0; i < 4; i++)
	{
		setColumnToZero(i);
		for (char j = 0; j < 4; j++)
		{
			if (isRowZero(j))
			{
				PORTC = ~_BV(j);
				_delay_ms(1000);
				PORTC = 0xff;
			}
		}
		setColumnToOne(i);

	}
}

void setup()
{
	DDRC = 0xff; // input
    timer1_init();
}
  
int main(void)
{
    
	setup();
  
    while(1)
    {
    }
}