PWM Duty problem

[sraiderk]

Timer 2 define the period of PWM.

set_pwm1_duty((int16)420); After that %50 ON %50 OFF signal of PWM one cycle pulse.

Then, I changed Timer2 frequency so, PWM period changed. Afterwords,set_pwm1_duty((int16)420); was not create %50 percent duty. I saw that pulse ON length is exactly same both frequency (T2). Only changing occurred at OFF cycle of PWM. I think same problem compiler side.

[sraiderk]

CCS C Version 5.076

[Ttelmah]

Not a compiler problem.

If you change the frequency, you have to change the numbers used for
given duty cycles:

setup_timer_2(T2_DIV_BY_1, NN, Y);

The second value here 'NN', is the 'PR2' value (it is called this in some of
the data sheets).

The value needed for a particular 'duty', is:

(PR2+1)*4*duty

So if PR2 was set to '209', then the value needed for 50%, would be

(210+1)*4*0.5 = 420

If you change your PR2 value to give twice the frequency, so PR2 = 104,
then to get 50% the duty value would need to change to:

(104+1)*4*0.5 =210

You have to calculate the value needed for a particular percentage on
time, dependant on the clock rate you are selecting.

[sraiderk]

Perfect explanation. Thank you...Sorry for I said the compiler problem...