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PWM Duty problem

 
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sraiderk



Joined: 09 Feb 2005
Posts: 48

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PWM Duty problem
PostPosted: Wed Feb 20, 2019 1:26 am     Reply with quote

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



Joined: 09 Feb 2005
Posts: 48

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PostPosted: Wed Feb 20, 2019 1:27 am     Reply with quote

CCS C Version 5.076
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Wed Feb 20, 2019 2:18 am     Reply with quote

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



Joined: 09 Feb 2005
Posts: 48

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PostPosted: Wed Feb 20, 2019 4:13 am     Reply with quote

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