// ------------------------------
//    ISR Test
// ------------------------------

volatile char isr_flag = 0;
volatile uint16_t count = 0;

void setup()
{
  Serial.begin(9600) ;   // festlegen der Baud-Rate

  TCCR1A = B00000000;
  TCCR1B = B00001011;    // Prescaler to 64; CTC on (Clear-Timer-on-Compare)
  OCR1BH = 0x00;
  OCR1BL = 0x00;
  TIMSK1 = (1<<OCIE1B);  // Output-Compare-Interrupt enable

  Serial.println ("\r\n\r\n");
  Serial.println ("--- ISR Test ---");
}/* --- setup --- */


void loop()
{
  if (isr_flag != 0)
  {
    Serial.print ("IRQ occured ");
    Serial.println (count);
    isr_flag = 0;
  }

}/* --- Ende Main Loop --- */


// ------------------------------
//   Timer1 ISR
ISR (TIMER1_COMPB_vect)
{
  isr_flag = 1;
  TCNT1 = 0;
  count++;
}