matrix.c

/* Row pin configuration
 * row: 0  1  2  3  4  5  6  7  8  9  10 11
 * pin: F0 F1 F4 F5 F6 F7 C6 C7 D5 D6 D7 E6
 */
static void unselect_rows(void)
{
    // Hi-Z(DDR:0, PORT:0) to unselect
    DDRF  &= ~0b11110011; // PF: 7,6,5,4,1,0
    PORTF &= ~0b11110011;
    DDRC  &= ~0b11000000; // PC: 7,6
    PORTC &= ~0b11000000;
    DDRD  &= ~0b11100000; // PD: 7,6,5
    PORTD &= ~0b11100000;
    DDRE  &= ~0b01000000; // PE: 6
    PORTE &= ~0b01000000;
}

static void select_row(uint8_t row)
{
    // Output low(DDR:1, PORT:0) to select
    switch (row) {
        case 0:
            DDRF  |= (1<<0);
            PORTF &= ~(1<<0);
            break;
        case 1:
            DDRF  |= (1<<1);
            PORTF &= ~(1<<1);
            break;
        case 2:
            DDRF  |= (1<<4);
            PORTF &= ~(1<<4);
            break;
        case 3:
            DDRF  |= (1<<5);
            PORTF &= ~(1<<5);
            break;
        case 4:
            DDRF  |= (1<<6);
            PORTF &= ~(1<<6);
            break;
        case 5:
            DDRF  |= (1<<7);
            PORTF &= ~(1<<7);
            break;
        case 6:
            DDRC  |= (1<<6);
            PORTC &= ~(1<<6);
            break;
        case 7:
            DDRC  |= (1<<7);
            PORTC &= ~(1<<7);
            break;
        case 8:
            DDRD  |= (1<<5);
            PORTD &= ~(1<<5);
            break;
        case 9:
            DDRD  |= (1<<6);
            PORTD &= ~(1<<6);
            break;
        case 10:
            DDRD  |= (1<<7);
            PORTD &= ~(1<<7);
            break;
        case 11:
            DDRE  |= (1<<6);
            PORTE &= ~(1<<6);
            break;
    }
}