volatile char *outA = (char*)0x22; // rows
volatile char *outB = (char*)0x25; // columns

void setup()
{
    volatile char *ddrA = (char*)0x21;
    volatile char *ddrB = (char*)0x24;
    *ddrA = 0xFF; // rows output
    *ddrB = 0xFF; // columns output
}

void delay_ms()
{
    volatile int i;
    for (i = 0; i < 3000; i++);
}

// 8x8 pattern for "C" (each byte = row data)
unsigned char C_pattern[8] = {
    0x3C, // 00111100
    0x42, // 01000010
    0x80, // 10000000
    0x80, // 10000000
    0x80, // 10000000
    0x42, // 01000010
    0x3C, // 00111100
    0x00  // empty row
};

void display_C_shift()
{
    int shift, col, repeat;

    // Shift from left to right (8 positions)
    for (shift = 0; shift < 8; shift++)
    {
        // Show each shifted position for some time
        for (repeat = 0; repeat < 80; repeat++)
        {
            for (col = 0; col < 8; col++)
            {
                *outB = 1 << col;               // select column
                *outA = ~(C_pattern[col] >> shift); // shift bits to move horizontally
                delay_ms();
            }
        }
    }
}

void loop()
{
    display_C_shift();
}