Hi,
200 Hz is OK. it makes 5ms for a total cycle.
Now you have to decide what resolution you need.
Maybe 5%. This gives 20 steps. 20 steps in 5ms.
Means you need to generate interrupt with 200Hz x 20 = 4000Hz.
This means you need to setup your timer to generate an interrupt eveery 250us.
Within the ISR you need a counter.
increment the counter every time you enter the ISR. set it to zero if it is >=19.
So it counts 0 up to 19.
Now you have to compare this counter with your PWM value. ( in the range of 0...20)
if pwm_value > counter then set PWM_PORT, else clear PWM_PORT.
return from ISR
****
0 gives 0% duty cycle
1 give 5% duty cycle
...
19 gives 95% duty cycle
20 gives 100% duty cycle.
*****
Klaus