PIC PWM help

[ptewright]

Hi,

I'm trying to setup a PIC for PWM. I want a period of 1 second. I am using a 4MHz clock. What values should PR2 and, TMR2 prescale should be used? If I want a 50% duty cycle, what values should CCPR1L and CCP1X and CCP1Y be? I'm having trouble calculating that.

Thanks

 

[williB]

i am just curious.. what ar ya ganna do with the pwm?
motor control?
.. just curious..

 

[Nigel Goodwin]

I'm trying to setup a PIC for PWM. I want a period of 1 second. I am using a 4MHz clock. What values should PR2 and, TMR2 prescale should be used? If I want a 50% duty cycle, what values should CCPR1L and CCP1X and CCP1Y be? I'm having trouble calculating that.

One second is far too low with a 4MHz clock, if you consult either the data sheet, or the midrange reference manual, it shows the formulas required, and gives example values.

As 'williB' mentioned, why do you want such a low PWM frequency?.

Is it just to flash an LED?.

 

[Oznog]

Hi,

I'm trying to setup a PIC for PWM. I want a period of 1 second. I am using a 4MHz clock. What values should PR2 and, TMR2 prescale should be used? If I want a 50% duty cycle, what values should CCPR1L and CCP1X and CCP1Y be? I'm having trouble calculating that.

Thanks

Too slow, I didn't do the math but that sounds bigger than the counter can do. This is the kind of thing you'd solve by setting a timer to create an interrupt like every 1/100th of a second (still 10k instruction cycles per interrupt). The ISR just has a counter to decide whether to reassign an output. PWM is not necessary.

And it doesn't have to be an even portion of a sec, the counter inside the ISR will just count something other than 1.

 

[ptewright]

pwm to set different frequencies

Basically, what i'm trying to do is setting the pwm for a certain frequency for about 0.5s, turning that off for 0.5s, so the period would be 1s. Then for the next period, I want to set the pwm to another frequency for 0.5s and turn that off for 0.5s.....etc.....
Is that possible with the PIC? I can't seem to get that working right.

 

[Nigel Goodwin]

Re: pwm to set different frequencies

Basically, what i'm trying to do is setting the pwm for a certain frequency for about 0.5s, turning that off for 0.5s, so the period would be 1s. Then for the next period, I want to set the pwm to another frequency for 0.5s and turn that off for 0.5s.....etc.....
Is that possible with the PIC? I can't seem to get that working right.

We've already told you that the PWM can't go that low with a 4MHz clock, just do it in software!.

You also didn't answer why you are trying to do this, it seems a pretty strange thing to want to do?. If you give exact details we may be able to make more informed suggestions.

 

[StupidDum]

set up a timer interrupt for, say, 5ms.
declare a variable and increment whenever interrupt occurs.
when the variable reaches 100, toggle the pin and reset the variable.