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   1 void setup() {
   2   // Set pin 13 to output
   3   pinMode(13, OUTPUT);
   4
   5   // Stop reception of interrupts
   6   noInterrupts(); //cli();
   7
   8   // Set PB1 to be an output (Pin9 Arduino UNO)
   9   DDRB |= (1 << PB1);
  10
  11   // Clear Timer/Counter Control Registers
  12   TCCR1A = 0;
  13   TCCR1B = 0;
  14   TIMSK1 = 0;
  15
  16   // Set non-inverting mode - Table 15-3 (page 108)
  17   TCCR1A |= (1 << COM1A1);
  18
  19   // Set Fast-PWM Mode (Mode 14) - Table 15-5 (page 109)
  20   TCCR1A |= (1 << WGM11);
  21   TCCR1B |= (1 << WGM12);
  22   TCCR1B |= (1 << WGM13);
  23
  24   // Clear Timer 1 Counter
  25   TCNT1  = 0;
  26
  27   // Set PWM frequency/top value - Output PWM 10kHz
  28   ICR1 = 199;   // Fclk_io / (Fout * Prescaler) - 1
  29   OCR1A = 100;  // Output OC1A will be ON for [OCR1A/(ICR1+1)]% of the time -> 100/(199+1) = 50%
  30
  31   // Enable compare match interrupt
  32   TIMSK1 |= (1 << OCIE1A);
  33   TIMSK1 |= (1 << TOIE1);
  34
  35   // Set prescaler to 8 and starts PWM
  36   TCCR1B |= (1 << CS11);
  37
  38   // Enables interrupts
  39   interrupts(); //sei();
  40 }
  41
  42 void loop() {
  43   // Empty
  44 }
  45
  46 //Timer1 Compare Match Interrupt turns OFF pin 13 (LED)
  47 ISR(TIMER1_COMPA_vect) {
  48   digitalWrite(13, LOW);
  49 }
  50
  51 //Timer1 Overflow Interrupt turns ON pin 13 (LED)
  52 ISR(TIMER1_OVF_vect) {
  53   digitalWrite(13, HIGH);
  54 }