Do I Have to Change Internal Interrupt Setups when I Change Clock Speed?
The equation for timer period is given by the following formula, where N is the value of the prescaler, TOP is the value given by either MAX (i.e. 0xFF, 0xFFFF) or the value in register OCRnx, and f is the frequency of the I/O clock.



If you're using phase-correct or phase- and frequency-correct mode, the factor (TOP+1) in the formula above should be replaced by 2&nbsp;×&nbsp;TOP.