Making PWM with analog input control in PIC18F4550

Question

I am trying to program with the PIC18F4550 a PWM with which I can regulate the duty-cycle with a variable resistance.

I attach my code to explain the problem I have.

#pragma config CPUDIV = OSC1_PLL2
#pragma config USBDIV = 1 
#pragma config FOSC = HS 
#pragma config FCMEN = OFF 
#pragma config IESO = OFF 
#pragma config PWRT = OFF 
#pragma config BOR = OFF 
#pragma config BORV = 3 
#pragma config VREGEN = OFF 
#pragma config WDT = OFF 
#pragma config WDTPS = 32768 
#pragma config CCP2MX = ON 
#pragma config PBADEN = ON 
#pragma config LPT1OSC = OFF 
#pragma config MCLRE = ON 
#pragma config STVREN = ON 
#pragma config LVP = ON 
#pragma config ICPRT = OFF 
#pragma config XINST = OFF 
#pragma config CP0 = OFF 
#pragma config CP1 = OFF 
#pragma config CP2 = OFF 
#pragma config CP3 = OFF 
#pragma config CPB = OFF 
#pragma config CPD = OFF 
#pragma config WRT0 = OFF 
#pragma config WRT1 = OFF 
#pragma config WRT2 = OFF 
#pragma config WRT3 = OFF 
#pragma config WRTC = OFF 
#pragma config WRTB = OFF 
#pragma config WRTD = OFF 
#pragma config EBTR0 = OFF 
#pragma config EBTR1 = OFF 
#pragma config EBTR2 = OFF 
#pragma config EBTR3 = OFF 
#pragma config EBTRB = OFF
#include <xc.h>
#define _XTAL_FREQ 20000000L
void ADC_Initialize()
{
 ADCON1bits.PCFG = 0;
 ADCON1bits.VCFG = 0;
 ADCON0 = 0;
 ADCON2bits.ACQT = 3;
 ADCON2bits.ADCS = 5;
 ADCON2bits.ADFM = 1;
 ADCON0bits.ADON = 1;
}
unsigned int ADC_Read(unsigned char channel)
{
 ADCON0 &= 0x11000101;
 ADCON0 |= channel<<3;
 __delay_ms(2);
 GO_nDONE = 1;
 while(GO_nDONE);
 return ((ADRESH<<8)+ADRESL);
}
#define TMR2PRESCALE 16
long PWM_freq = 8000;
void PWM_Initialize()
{
 PR2 = 0x26;
 CCPR1L = 1;
 TRISCbits.RC1 = 0;
 TRISCbits.RC2 = 0;
 T2CON = 0x03; 
 CCP1CON = 0x0C;
 TMR2 = 0;
 T2CONbits.TMR2ON = 1; 
}
void PWM_Duty(unsigned int duty)
{
 if(duty<1023)
 {
 duty = ((float)duty/1023)*(_XTAL_FREQ/(PWM_freq*TMR2PRESCALE));
 CCPR1L = duty>>2;
 }
}
void main()
{
 int adc_value; 
 TRISC = 0; 
 TRISA = 1; 
 TRISD = 0; 
 ADC_Initialize(); 
 PWM_Initialize(); 
 do
 {
 adc_value = ADC_Read(4);
 PWM_Duty(adc_value); 
 __delay_ms(50); 
 }while(1);
}

If I execute the above code, what I have at the output of the PWM are 0v and a frequency 0. As shown in the following image

enter image description here

If in the fixed code the value of the PWM Duty (580), for example.

Then I stop running the analog input.

So it seems that the PWM signal is regulated and I have a voltage at the output.

As I show in the following image.

enter image description here

What I do not understand is that in neither of the 2 cases the frequency is 0, when it should be approximately 8000Hz.

On the other hand I see that if I set the duty_cycle it seems that it regulates and gives voltage to the output.

So there must be a fault in the part of the analog input that I have not been able to find.

Finally, I leave a picture of the circuit.

enter image description here

• Mike: PR = 0x26 that don't make any sense for me. Another case: Why the cast to float?
• Geo: Is the result of the calculation: PWM periodo = (PR2 + 1)*4*Tosc*Prescaler -> 1/8KHz = (PR2 + 1)*4*(1/20MHZ)*16 -> PR2 + 1 = 39.06 -> PR2 = 38.06 = 38 -> 26 hex -> PR = 0x26
• Geo: I have tried with the parameter PR2 = 0x3FF and the same thing happens
• Mike: duty = ((float)duty/1023)*(_XTAL_FREQ/(PWM_freq*TMR2PRESCALE)); This part is also wrong. Just CCPR1L = duty>>2;.Have a look into the datasheet.
• Geo: Thanks for the help. I have already got it working. Apart from the errors mentioned above I also found this ADC_Read (0).

Answer 1

With the following code I could make it work

#define TMR2PRESCALE 16
long PWM_freq = 8000;
void PWM_Initialize() 
{
 PR2 = ("%#x", (_XTAL_FREQ/(PWM_freq*4*TMR2PRESCALE)) - 1); //Setting the PR2 formulae using Datasheet 
 CCPR1L = 0x1F;
 TRISCbits.RC1 = 0; 
 TRISCbits.RC2 = 0;
 T2CON = 0x03; 
 CCP1CON = 0x0C;
 TMR2 = 0;
 T2CONbits.TMR2ON = 1; 
}
void PWM_Duty(unsigned int duty)
{
 if(duty < 1023)
 {
 duty = ((float)duty/1023)*(_XTAL_FREQ/(PWM_freq*TMR2PRESCALE));
 CCPR1L = duty>>2;
 }
}
void ADC_Initialize()
{ 
 ADCON1bits.PCFG = 0;
 ADCON1bits.VCFG = 0;
 ADCON0 = 0;
 ADCON2bits.ACQT = 3;
 ADCON2bits.ADCS = 5;
 ADCON2bits.ADFM = 1;
 ADCON0bits.ADON = 1;
}
unsigned int ADC_Read(unsigned char ch)
{
 if(ch > 13)return 0;
 ADCON0 = 0;
 ADCON0 = (ch<<2);
 ADCON0bits.ADON = 1;
 ADCON0bits.GO_DONE = 1;
 while(ADCON0bits.GO_DONE == 1);
 ADCON0bits.ADON = 0;
 return ADRES;
}
void main()
{ 
 int adc_value; 
 TRISC = 0;
 TRISA = 1;
 TRISD = 0; 
 ADC_Initialize();
 PWM_Initialize();
 do
 {
 adc_value = ADC_Read(0);
 PWM_Duty(adc_value); 
 __delay_ms(50); 
 }
 while(1); //Infinite Loop 
}