#include <Arduino.h>

void setupTimer3(){
  noInterrupts();
    TCCR3A = 0;
    TCCR3B = 0;
    TCNT3 = 0;
  
  OCR3A = 15624;

  TCCR3B |= (1 << WGM32);
  TCCR3B |= (1 << CS32) | (1 << CS30);
  TIMSK3 |= (1 << OCIE3A);
  interrupts();

}


void setup() {
  DDRC = 0xFF; 
  setupTimer3();
}

void loop() {
  PORTC = (1<<PC4) | (1<<PC5) |(1<<PC6) |(1<<PC7);
  delay(2000);
  PORTC = (0<<PC4) | (0<<PC5) |(0<<PC6) |(0<<PC7);
  delay(2000);
  }

ISR(TIMER3_COMPA_vect){
  PORTC ^= (1<<PC0) | (1<<PC1) |(1<<PC2) |(1<<PC3);
}