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120 KHz Carrier Signal using pwm module of pic 16f877

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iruraz

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Hi Everyone,

I try to obtain 120 KHz carrier signal with using pwm module of pic 16f877 . PWM uses timer2 and maximum frequency value is 250 Hz because pr2 maximum value is 255 and postscale maximum value is 16. And the formula is :

Tpwm=Tcommand*(pr2 + 1)*(tmr2 division ratio)

And here is the code below. How can i obtain 120KHz signal with pwm. By the way i work with ccs-c

regards
Code: 
#include <16f877.h>   

#fuses XT,NOWDT,NOPROTECT,NOBROWNOUT,NOLVP,NOPUT,NOWRT,NODEBUG,NOCPD

#use delay (clock=4000000) 

#use fast_io(c) 

void main ( )
{
   setup_psp(PSP_DISABLED);       
   setup_spi(SPI_SS_DISABLED);     
   setup_timer_1(T1_DISABLED);     
   setup_adc_ports(NO_ANALOGS);    
   setup_adc(ADC_OFF);             

   set_tris_c(0x00); 

   setup_ccp1(CCP_PWM);  

   setup_timer_2(T2_DIV_BY_16,255,16); 

   set_pwm1_duty(30); 

   while(1);

}
 

120 KHz Carrier Signal - help needed

Hi,
With PIC16F877, the maximum frequency possible with CCP module is 20kHz. For frequencies greater than that you need to use PIC18/24/dsPIC etc.

Hope this helps.
Tahmid.
 

Re: 120 KHz Carrier Signal - help needed

done exactly with a 12MHz clock.
you should adjust the clock as we dont get exactly 120khz

Code: 
' Timer0 Registers: 
' Prescaler=1:1; TMR0 Preset=231; Freq=120 000,00Hz; Period=8 333 ns
OPTION_REG.T0CS = 0 ' bit 5 TMR0 Clock Source Select bit:0=Internal Clock (CLKO) / 1=Transition on T0CKI pin
OPTION_REG.T0SE = 0 ' bit 4 TMR0 Source Edge Select bit: 0=low/high / 1=high/low
OPTION_REG.PSA  = 1 ' bit 3 Prescaler Assignment bit: 0=Prescaler is assigned to the Timer0
OPTION_REG.PS2  = 0 ' bits 2-0  PS2:PS0: Prescaler Rate Select bits
OPTION_REG.PS1  = 0 
OPTION_REG.PS0  = 0 
TMR0 = 231            ' preset for timer register

this program should help you a lot:
**broken link removed**
warning: there seems to be a bug there you should set the date of your computer to 2009. dont want to start for me if it is 2010 ...

Added after 3 hours 6 minutes:

and these are the settings with timer 2 :

Code: 
' Timer2 Registers:
' Prescaler=1:1; TMR2 PostScaler=1:1; PR2=25 - Freq = 120 000,00Hz - Period = 8 333 ns
'T2CON |       = 0 ' bits 6-3 Post scaler 1:1 thru 1:16
'T2CON.TOUTPS3 = 0 
'T2CON.TOUTPS2 = 0 
'T2CON.TOUTPS1 = 0 
'T2CON.TOUTPS0 = 0 
'T2CON.TMR2ON  = 1 ' Timer2 on bit: 1=Timer2 is on;
'T2CON.T2CKPS1 = 0 ' bits 1-0  Prescaler Rate Select bits
'T2CON.T2CKPS0 = 0 
T2CON = %00000100
PR2 = 25            ' PR2 (Timer2 Match value)
 

120 KHz Carrier Signal - help needed

the program is effectively stuck to work only if the date of the computer is 2009 ...
 

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