You will need PeriodValue clock counts for a complete PWM period. The compare value must be between 0 and the period value to set the duty-cycle between 0 and 100 percent.
Sorry I am still confused.
Suppose I set PWM to 100 and PeriodValue clock to 100Hz. What does this mean?
PWM clock = 100Hz (quite slow) / Period value 100 results in a 1Hz PWM signal. By setting the compare value betweem 0 and 100 you can control the duty-cycle.
Besides this explanation, tell a bit more what you want to perform with your PWM.