using the pwm's in pic18f2431-2331-4331-4431

[mystified]

Thanks did not know that ccp and pwm0-5 are not the same pins that helped now how about setuo for timer 2.

[Bruce]

If you're using HPWM you don't need to mess with Timer2. It's automatically handled
for you.

If you plan to setup hardware PWM manually, these calcs should help.

PR2=(Fosc/(4*PS*Freq))-1
TMR2 Prescaler = 1 PR2 = (8MHz/(4*1*12,000)) = (8MHz/48,000)-1 PR2 = 165.666
TMR2 Prescaler = 4 PR2 = (8MHz/(4*4*12,000)) = (8MHz/192,000)-1 PR2 = 40.666
TMR2 Prescaler = 16 PR2 = (8MHz/(4*16*12,000))-1 = (8MHz/768,000))-1 PR2 = 9.416

CCPR1L:CCP1CON<5:4>=(PR2+1)*4*Duty%
(165+1)*4*0.5 = 332
(40+1)*4*0.5 = 82
(9+1)*4*0.5 = 20

To load the duty cycle registers just place the value calculated in a word, and
do something like this;

Duty = 332              ' Roughly 50% duty cycle
CCP1CON.4 = Duty.0	' Setup 10-bit duty cycle as
CCP1CON.5 = Duty.1	' a 10-bit word
CCPR1L = Duty >> 2

Search here for HPWM and you'll find a boat-load more examples.

[Cyborg]

Hi Bruce,

you mentioned above that the equation used to calculate the PWM resolution is

log(20MHz/19.455kHz) 3.01
Resolution = ------------------ = ----------- = 10 bits
.301 .301

In the 18F2431 datasheet it says that Fosc must be divided by four, i.e.

log(5MHz/19.455kHz) 2.41
Resolution = ------------------ = ----------- = 8 bits
.301 .301

and in other microchip document (link below) it provides the same equation you used.
http://ww1.microchip.com/downloads/e...doc/31014a.pdf

I am confused here! Can you please tell me what you think of that?

Kind regards,

[Bruce]

Look at equation 17-4 PWM RESOLUTION. Then look at Table 17-2 just below it.

Try plugging in some numbers on your calculator using both methods, and see what you get according to the resolutions shown in Table 17-2 for different values of Fosc, at various frequencies.

[Cyborg]

You are right. So for 10 bits, thats 2 LSBs of PDCxH and 8 bits of PDCxL. Thanks.

[Bruce]

So for 10 bits, thats 2 LSBs of PDCxH and 8 bits of PDCxL

PDCxH gets the 2 MSBs. PDCxL the lower 8-bits.

[park21]

hello bruce
i have a doubt abt carrier generation in 18f4431.sine wave ne how il generate through luk up table bt m nt bin able to generate carrier frequency of 20khz to compare it with ma sine wave.i'm attaching image for ur reference.can u plz help me in dis .

[camerart]

Hi,
Finding this old thread may have answered some questions, I wanted to know, so thanks for it, especially Bruce.
Cheers, Camerart.