tdquadros:
I need something between 80 and 250 (8 bit resolution). This is one of my controlled variables. It must change the value based on the control law every second.
That is not the PWM frequency but (part of) the duty cycle.
To select a different frequency, you had better using PWM library or TC library from antodom or make some direct register programming with the PWM peripheral or the timer counter peripheral.