void setup() {
  
}

void loop() {
  delay(1000);
  int seconds = 0;
  int minutes = 0;
  int hours = 0;

  seconds++;
  if(seconds == 60){
    seconds = 0;
    minutes++;
    if(minutes == 60){
      minutes = 0;
      hours++;
      if(hours == 24){
        hours = 0;
      }
    }
  }

PORTD = (seconds/10) << 4 + seconds%10 + (minutes%2) << 7;
PORTC = (hours/10) << 4 | (hours%10);
PORTB = (minutes/10) << 3 | (minutes%10) >> 1;

}