//Timer programming with LED of freq 200Hz
void timer3();
void setup() {
  DDRB |= (1<<7);
}

void loop() {
  timer3();
  PORTB |= (1<<7);
  timer3();
  PORTB &= ~(1<<7);
}

void timer3()
{
  TCCR3A= 0x00;
  TCCR3B= 0x01;
  TCNT3H= 0x63;
  TCNT3L= 0xC0;
  while((TIFR3 & (1<<TOV3))==0);
  TCCR3B= 0;
  TIFR3= 1<<TOV3; 
}