const uint8_t row_pins[4] = {4, 5, 6, 7};
const uint8_t col_pins[6] = {8, 9, 10, 11, 12, 11};
volatile uint8_t row_cnt = 0;
uint8_t col_cnt = 0;
uint8_t row_cnt2 = 23;

#define rowClkPin A0

volatile bool matrixImage[4][6] = {
  1, 0, 1, 0, 1, 0,
  0, 0, 0, 0, 0, 0,
  0, 1, 0, 1, 0, 1,
  0, 0, 0, 0, 0, 0

};

ISR(TIMER0_COMPA_vect) {   //This is the interrupt request

  if (col_cnt < 6) {
    col_cnt++;
  } else {
    col_cnt = 0;
  }
  switch (row_cnt) {
    case 0:
      PORTD = B00010000;
      row_cnt = 1;
      break;
    case 1:
      PORTD = B00100000;
      row_cnt = 2;
      break;
    case 2:
      PORTD = B01000000;
      row_cnt = 3;
      break;
    case 3:
      PORTD = B10000000;
      row_cnt = 0;
      break;
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(rowClkPin,OUTPUT);
  for (uint8_t i = 0; i < 4; i++) {
    pinMode(row_pins[i], OUTPUT);
    digitalWrite(row_pins[i], LOW);
  }
  Serial.println("");

  for (uint8_t i = 0; i < 6; i++) {
    pinMode(col_pins[i], OUTPUT);
    digitalWrite(col_pins[i], LOW);
  }
  Serial.println("pins set");


  TCCR0A = (1 << WGM01); //Set the CTC mode
  OCR0A = 0xF9; //Value for ORC0A for 1ms

  TIMSK0 |= (1 << OCIE0A); //Set the interrupt request
  sei(); //Enable interrupt

  TCCR0B |= (1 << CS02);
  TCCR0B |= (0 << CS01); //Set the prescale 1/265 clock
  TCCR0B |= (0 << CS00);

}

void loop() {
 digitalWrite(rowClkPin,!digitalRead(rowClkPin));
}