PWM (Pulse Width Modulation) General Discussion on Phase Correct PWM

Phase Correct PWM is just the pulse positioned at the middle of the period. The timer/counter is able to do this because instead of the timer overflowing and resetting the count to 0, it counts backward back to 0. With the 8-bit timer, the OCR (Output Compare Register) can be used to create this pulse. When the timer arrives to the OCR value as it counts up, the pulse starts. The timer will start to count downward and will hit the OCR value again, the pulse will end. This creates a symmetrical characteristic with the counting and pulse, so the pulse is at the middle of the period. This can also be done with the 16-bit timer/counter and would be more versatile with the ICR (Input Capture Register) being the top of the count (where the count starts to count downward) and the OCR value as the start and end of the pulse.