Hi,
OK, lots of questions....Lets take a step back and look at how the PWM module works - basically.
There's a timer (PTMR), a period register (PTPER) - these are common for all "channels". Then there are a 4 dutycycle registers and comparators.

The timer starts at 0 and counts up until its value equals that of the period register, it then starts over at 0 and it all repeats. If you load the period register with the value 150 the timer will count from 0 to 150 and then start over at 0, count to 150 and so on. If the timer is driven with a frequency of 1MHz it will count to 150 in 151us so the PWM frequency 6622Hz.

When the timer starts at 0 the PWM output is set. As the timer counts upwards its value is compared to that of the dutycycle register. When the two are equal the PWM output is reset.

So, if you load the period register with 150 and the dutycycle register with 50 you'll get a dutycycle of ~33% because the PWM period is divided into 151 steps. If you now change the value of period register to 499 the PWM frequency will change because it now takes 500us (instead of 151) to reach its destination and the dutycycle will change to 10% because there's now 500 steps in the cycle compared to 151 before. (This again asumes a 1MHz frequency being fed to the timer and is only meant to describe how the PWM generation works).

So, as you probably can see, the absolute value of the dutycyle register at which you'll get 100% dutycycle is equal to that of that of the period register.

This is basically how it works.

/Henrik.