// Timer Interrupts by ISR
// 


// Variables
bool LED_STATE = LOW; 

void setup() {
  
  pinMode(5, OUTPUT);
  cli(); // 

  TCCR1A = 0;
  TCCR1B = 0;

  // 2  Set the prescalar to desired value
  TCCR1B |= B00000100; // Set CS12 to prescalar 256
  // TIMSK1 |= (1 << CS12);

  // 3  Enable compare match mode on register A
  TIMSK1 |= B00000010;  // Set OCIE1A to 1 
  // TIMSK1 |= (1 << OCIE1A); 

  // 4
  OCR1A = 31250;
  sei();  // 

}

void loop() {
  // put your main code here, to run repeatedly:

}

// 5 ISR will trigger each 500ms
ISR(TIMER1_COMPA_vect) {
  TCNT1 = 0;
  LED_STATE = !LED_STATE;
  digitalWrite(5, LED_STATE);
}