Programming: Fast PWM (Pulse Width Modulation) with Interrupts and No Prescaling

The interrupts library must be included. The OCIE1A (Output Compare Interrupt Enable) is set in the TIMSK1 (Timer mask) register to enable the interrupts for the timer/counter when the ICR (Input Capture Register) is reached. The Global Interrupt is used sei();. When the ICR value is reached, the ISR (Interrupt Service Routine) for the TIMER1_COMPA_vect is called.