unsigned char odczytaj_klawiature()
{
    unsigned char result = 0xFF;
    unsigned char i, j;

    PORTA = 0xFF;
    for(i = 0; i < 4; i++)
    {
        DDRA = (1<<i+4);
        PORTA = ~(1<<i+4);
        for(j = 0; j < 4; j++)
        {
            _delay_ms(2);
            if(!(PINA & (1<<j)))
            {
                _delay_ms(2);
                result = PINA;
            }
        }

    }
    switch(result)
    {
        case 0b11101110:
            result=1; break;
        case 0b11011110:
            result=2;break;
        case 0b10111110:
            result=3; break;
        case 0b01111110:
             result=4; break;
        case 0b11101101:
            result=5; break;
        case 0b11011101:
             result=6; break;
        case 0b10111101:
            result=7; break;
        case 0b01111101:
            result=8; break;
        case 0b11101011:
             result=9; break;
        case 0b11011011:
           result=10; break;
        case 0b10111011:
            result=11; break;
        case 0b01111011:
            result=12; break;
        case 0b11100111:
            result=13; break;
        case 0b11010111:
            result=14; break;
        case 0b10110111:
            result=15; break;
        case 0b01110111:
            result=16; break;
        case 0b11111111:
            result=0; break;
        default:
        result=31; break;
    }
	return result;
}