PWM problem pic16f1825

[alexandru321]

hello guys i have some problem with pwm ,i want to control a servo motor with adc ,i cant make 20 ms period....i tried but max is 16 ms...i don t know wath i do wrog ,pls help.

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#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = ON       // Power-up Timer Enable bit (PWRT enabled)
#pragma config BOREN = OFF      // Brown-out Reset Enable bit (BOR disabled)
#pragma config LVP = ON         // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3/PGM pin has PGM function; low-voltage programming enabled)
#pragma config CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
#define _XTAL_FREQ 20000000
#define TMR2PRESCALE 4
#include"pic16f1825.h"
#include <xc.h>
 
long PWM_freq = 5000;
long PWM_period;
PWM_Initialize()
{
      
    PR2 =(_XTAL_FREQ/(PWM_freq*4*TMR2PRESCALE)) - 1; //Setting the PR2 formulae using Datasheet // Makes the PWM work in 5KHZ
    CCP4M3 = 1; 
    CCP4M2 = 1;
    T2CKPS0= 1;
    T2CKPS1= 1;
    TMR2ON= 1; //Configure the Timer module
    TRISC1=0; 
 
}
 
PWM_Duty(unsigned int duty)
{
      if(duty<1023)
  {
 
    duty = ((float)duty/1023)*(_XTAL_FREQ/(PWM_freq*TMR2PRESCALE)); 
    DC4B1 = duty & 1;
    DC4B0 = duty & 2; 
    CCPR1L = duty>>2;
    
  }
}
 
void ADC_Initialize()
{
  ADCON0 = 0b0000001; //ADC ON and Fosc/16 is selected
  ADCON1 = 0b11010000;
}
unsigned int ADC_Read(unsigned char channel)
{
  ADCON0 &= 0x11000101; //Clearing the Channel Selection Bits
  ADCON0 |= channel<<3; //Setting the required Bits
  __delay_ms(2); 
  GO_nDONE = 1; //Initializes A/D Conversion
  while(GO_nDONE); //Wait for A/D Conversion to complete
  return ((ADRESH<<8)+ADRESL); //Returns Result
}
 
void main()
{
   int adc_value;
   int pot;
  TRISC = 0x00; //PORTC as output
  TRISA = 0xFF; //PORTA as input
  //TRISD = 0x00;
  ADC_Initialize(); //Initializes ADC Module
  PWM_Initialize();  //This sets the PWM frequency of PWM1
 
  do
  {
    adc_value =0.01825*ADC_Read(0)+7;
     pot =170 -adc_value ;
    __delay_ms(5);  //Reading Analog Channel 0 
    PWM_Duty(adc_value);
      __delay_ms(50); 
      
  }while(1); //Infinite Loop
  
}

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[KlausST]

Hi,

you say 20ms, this is 50Hz,
but in your code I see 5000Hz, this is 200us

What do you want now?

 

[alexandru321]

hi,i set 50 hz but the period is 10 ms ,i dont know were is the problem,may be from prescaler or timer?

 

[KlausST]

Hi,

Please confirm that the chip runs with 20MHz and there is no clock divider involved.

Klaus

 

[paulfjujo]

hello,


at FOSC 20MHz
you can't reach as low value of 20mS


at 4MHz , i can get a maximum of 16mS, using MikroC PWM library, only if i modify "Pre" and "Post" divider of PR2 register
with a PIC12F1840..

you better have to use 2 timers , one for 20mS cycle , other one for the commande from 1 to 2 mS.

 

[Aussie Susan]

You have set the oscillator to HS but there is no crystal in your schematic. Therefore it is probably some artifact of the simulator that is providing you with a primary clock source and that could be any frequency.
You need to actively set the oscillator correctly. The use of the <xc.h> include makes me think you are using the XC8 compiler - just in case you misunderstand this (many do when starting out with the XC-series compilers) the _XTAL_FREQ define is not used by anything except the compiler-supplied delay macros and whatever you put into your code.
Susan