PWM frequency problem PIC MicroC

[Pravin Gosavi]

Hello I want to generate a PWM for my application. I am using PIC16F1939, MicroC and PICkit 2 to burn the program.

Here's my code-

void interrupt()

{

if (TMR2IF_bit == 1)

{

CCPR1L = 100;

TMR2IF_bit = 0;

}

}


void main()

{

C1ON_bit = 0;

C2ON_bit = 0; // Disable Comparators

TRISC = 0XFF;

PR2 = 249;

CCP1CON = 12;

CCPR1L = 0;

TMR2IF_bit = 0;

T2CON = 0X04;

while (TMR2IF_bit == 0);

TMR2IF_bit = 0;

TRISC = 0X00;

TMR2IE_bit = 1;

GIE_bit = 1;

PEIE_bit = 1;
while(1)
{
//Do other stuff
}
}

I replaced old crystal with a new one still no change. Crystal is 20MHZ. Frequency I get on the CCP pin is 500HZ only where according to the calculations it should be 20 KHZ. Also I replaced PIC16F1939 with PIC16F877A.
Where could be the problem? Please help!

 

[Pommie]

You might have the internal 32kHz oscillator selected. Try blinking an LED to work out the actual oscillator frequency.

Mike.

 

[Pravin Gosavi]

I have selected HS oscillator and inserted 20MHz in the sidebar in MicroC. Is PICkit 2 overriding the settings? How to select HS oscillator in PICkit 2 and in MicroC.

 

[Pommie]

Don't do MikroC. Try flashing an LED.

Mike.

 

[Pravin Gosavi]

With what? PWM? Or with delay function??

 

[Pommie]

With delay. If you try for 1 Hz and you get a flash every 150 seconds then you have the 32kHz oscillator.

Or, try switching to the internal oscillator. Use the 16MHz as it's nearest.

Mike.

 

[Pravin Gosavi]

Thanks for your quick replies. I programmed the PIC with simple program-

PORTD= 0XFF;
delay_ms (10);
PORTD= 0X00;
delay_ms (10);

I am getting 1HZ blink while it should be with delay_ms (1000)? So I think PIC is being programmed with internal oscillator. But I have selected HS in MICROC config settings. Is PICkit 2 overriding config bits? Where can set them manually? I couldn't find any option?

 

[Ian Rogers]

How to select HS oscillator in PICkit 2 and in MicroC.

Its in the project settings... Nothing to do with pickit2..

 

[Pravin Gosavi]

Its in the project settings... Nothing to do with pickit2..

View attachment 105227

Thanks. I have tried it already. I think the crystal oscillator is not working. I got my program working by using internal oscillator. For those who want to know the settings, use - OSCCON = 0X7A for selecting 16MHZ internal oscillator ( May be for PIC16F1939 only. Check datasheet for other PICs). Thank you all. I will let you know when I'll replace the crystal.

 

[Pommie]

Do you have the required capacitors on the crystal?

Mike.

 

[Pravin Gosavi]

Yes 22 pf. What do you mean by "Required"? Do we need to calculate it?

 

[Ian Rogers]

Do we need to calculate it?

Yep but 15 ~ 33pf is the norm for a 20Mhz.. I have use 22pf for years without issue..