keypadavrc

//Cezary Zaprawa

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

volatile uint8_t columnPosition = 0;
volatile uint8_t rowPosition = 0;

ISR(TIMER1_OVF_vect) {
    DDRA = (1 << columnPosition);
    PORTA = ~(1 << columnPosition);
    if((PINA & 0xf0) != 0xf0) {
        rowPosition = PINA;
        if(!(rowPosition & (1 << 4))) rowPosition = 0;
        else if(!(rowPosition & (1 << 5))) rowPosition = 1;
        else if(!(rowPosition & (1 << 6))) rowPosition = 2;
        else if(!(rowPosition & (1 << 7))) rowPosition = 3;
        PORTD = rowPosition*4 + columnPosition;
    }
    columnPosition++;
    if(columnPosition == 4) columnPosition = 0;
}

void init() {
    cli();
    ICR1 = 15625;
    TCCR1A |= (1 << WGM11);
    TCCR1B |= (1 << WGM12) | (1 << WGM13) | (1 << CS11) | (1 << CS10);
    TIMSK |= (1 << TOIE1);

    DDRD = 0xFF;
    DDRA = 0x0F;
    PORTA = 0xFF;
    PORTD = 0xFF;

    sei();
}

int main(void) {
    init();
    while(1) {
        asm("nop");
    }
}