Can the PWM output be forced to "Low level" and “High level”?
Yes. To force the PWM output to "Low level", set the Pulse Output Mask bit (PMSK) of the Timer Control Register (TMCR) to "1". Another option is to set the PWM duty value to "current duty value > cycle value" while outputting the PWM signal, which forces the output to "Low level" when the next underflow event occurs.
To force the PWM output to "High level" (= 100% Duty pulse), set the same values for the PWM Cycle Setting Register (PCSR) and the PWM Duty Setting Register (PDUT). This forces the output to "High level" when the next underflow event occurs.