Wrong Frequency

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- 4th December 2010, 12:27
gadelhas

Wrong Frequency

Hi Everyone;

I've got this code, and it's working fine, however the frequency of the pwm mesured with the oscilocope it's half the frequency configured.
It is suposed to have 5Khz, however i've got 2.5Khz.

Can anybody tell me what i'm doing wrong in the code?

PIC12F683

Code:

Define OSC 8 @ __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_OFF & _CP_OFF & _BOD_OFF ' PINOUT 1 = IN; 0 = OUT ' ==================================================================== '76543210 TRISIO = %00000001 '76543210 GPIO = %00000000 ANSEL = 1 'GP0 ANALOG VRCON = 0 'VREF OFF CMCON0 = 7 'COMPARATOR OFF ADCON0 = %10000000 'RIGHT JUSTIFY - 128 PR2 = %00011000 'SET 24 - 5000Hz - 8Bits T2CON = %00000110 'TIMER2 ON - PRESCALER 1:16 - Max Duty Value 100 - 1% Step CCPR1L = %00000000 CCP1CON = %00001100 'PWM ON

Thanks
- 4th December 2010, 12:52
aratti

You have to set the OSCCON register, since by default is set to 4 MHz and you define the osc as an 8 MHz one.

Cheers

Al.
- 4th December 2010, 13:07
gadelhas

Thank you aratti for the fast answer to my problem. I changed the OSCCON register, and it worked at the desired frequency.

Thank you once again!
- 5th December 2010, 03:31
rsocor01

Hmmm :confused:, I thought the DEFINE OSC x takes care of the frequency registers. I'm just curious, will it work if the internal oscillator is defined first and then the frequency is defined after that? In the next code, I just swapped the order of the first two lines in gadelhas original code.

Code:

@ __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_OFF & _CP_OFF & _BOD_OFF Define OSC 8 ' PINOUT 1 = IN; 0 = OUT ' ==================================================================== '76543210 TRISIO = %00000001 '76543210 GPIO = %00000000 ANSEL = 1 'GP0 ANALOG VRCON = 0 'VREF OFF CMCON0 = 7 'COMPARATOR OFF ADCON0 = %10000000 'RIGHT JUSTIFY - 128 PR2 = %00011000 'SET 24 - 5000Hz - 8Bits T2CON = %00000110 'TIMER2 ON - PRESCALER 1:16 - Max Duty Value 100 - 1% Step CCPR1L = %00000000 CCP1CON = %00001100 'PWM ON

Robert
- 5th December 2010, 11:15
mackrackit

The configs and the OSCCON register if using an internal OSC is for setting the hardware.
The PIC will then run at that speed. Run at the speed of the external OSC or the internal setup.

All
DEFINE OSC X
does is to tell PBP how fast the chip is running. DEFINE OSC X does not set the chips speed.

Because the two are completely different things the order does not matter.
- 6th December 2010, 02:19
rsocor01

Quote:

Originally Posted by mackrackit

The configs and the OSCCON register if using an internal OSC is for setting the hardware.
The PIC will then run at that speed. Run at the speed of the external OSC or the internal setup.

All
DEFINE OSC X
does is to tell PBP how fast the chip is running. DEFINE OSC X does not set the chips speed.

Because the two are completely different things the order does not matter.

Ooh, I see. Dave thank you for your help.

Robert