PIC18F26K20 PWM Configuration

Question

I am working with PIC18F26K20 and MPLABX IDE. I wrote some code for configuring and running the PWM. However, The output I get is at 50 percent duty Cycle no matter what duty cycle I provide the application. Following is the code I have written. The description of what I have done is included in the comments:

# define TMR2Prescalar 2

// 1 - Disable the PWNM Pin
TRISCbits.RC1 = 1;

// 2 - Not used since I'm using CCP not ECCP

// 3 - Set PWNM Period by setting PR2
//The formula is as given in the datasheet of PIC18F26k20 on page 141
// PR2 = (Fosc/(4*PWM frequency* TMR2 Prescalar)) -1
PR2 = (_XTAL_FREQ)/(4* 1000 * TMR2Prescalar);

// 4 - Configure the CCP module for the PWM mode by loading the CCPxCON register with the appropriate values
CCP2CON = CCP2CON | 0x0F;

// 5 - Set the PWM duty cycle by loading the CCPRxL register and CCPx bits of the CCPxCON register
// According to the datasheet page 141,  CCPRxL:DCxB<1:0> = (PulseWidth * Fosc) / TMR2Prescalar
uint16_t bits = 0;
// 70 percent pulse width
bits = (70* _XTAL_FREQ)/ TMR2Prescalar;
//Loading values into appropriate registers
CCP2CONbits.DC2B0 = bits & 0x0001;
CCP2CONbits.DC2B1 = bits & 0x0002;
CCPR2L = bits >> 2;

// 6 - Configure and start Timer2:
// Clear the TMR2IF interrupt flag bit of the PIR1 register
PIR1bits.TMR1IF = 0;
// Set the Timer2 prescale value by loading the T2CKPS bits of the T2CON register
T2CONbits.T2CKPS = 0;

//Enable Timer2 by setting the TMR2ON bit of the T2CON register.
T2CONbits.TMR2ON = 1;

// Wait until Timer2 overflows (TMR2IF bit of the PIR1 register is set).
while (!PIR1bits.TMR2IF);

//Enable the CCPx pin output driver by clearing the associated TRIS bit.
TRISCbits.RC1 = 0;

I am using an internal oscillator. The code for configuring internal oscillator is given below:

void OSCILLATOR_Initialize(void)
{
    // SCS INTOSC; OSTS intosc; IRCF 8MHz_HFINTOSC/2; IDLEN disabled; 
    OSCCON = 0x62;
    // INTSRC disabled; PLLEN disabled; TUN 0; 
    OSCTUNE = 0x00;
    // Set the secondary oscillator 
}

Can anyone tell me whats wrong with the above code?

Answer 1

Your code fragments do not have enough context to sort out what you may be doing wrong.

This code seems to work for me:

/*
 * File: main.c
 * Target: PIC18F26K20
 * IDE: MPLABX v5.10
 * Compiler: XC8 v2.05
 * 
 * Description:
 *  Initialize PWM1 for output on PORTC pin RC2
 *  Initialize PWM2 for output on PORTC pin RC1
 *
 */
#include <xc.h>
/*
 * PIC configuration words
 */
#pragma config FOSC = INTIO67, FCMEN = OFF, IESO = OFF, BOREN = OFF
#pragma config WDTEN = OFF, WDTPS = 1024, PBADEN = OFF, HFOFST = ON
#pragma config LVP = OFF, STVREN = ON, XINST = OFF
#pragma config CP0 = OFF, CP1 = OFF, CP2 = OFF, CP3 = OFF
#pragma config CPB = OFF, CPD = OFF
#pragma config WRT0 = OFF, WRT1 = OFF, WRT2 = OFF, WRT3 = OFF
#pragma config WRTC = OFF, WRTB = OFF, WRTD = OFF
#pragma config EBTR0 = OFF, EBTR1 = OFF, EBTR2 = OFF, EBTR3 = OFF
#pragma config EBTRB = OFF
#pragma config PWRT = OFF, BORV = 18, MCLRE = ON, CCP2MX = PORTC
#pragma config LPT1OSC = ON
/*
 * Target specific libraries
 */
#include <xc.h>
/*
 * Standard libraries
 */
#include <stdint.h>
/*
 * Constants
 */
#define _XTAL_FREQ 8000000L
#define FCYC (_XTAL_FREQ/4L)
/*
 * Initialize this PIC hardware
 */
void Init_PIC(void)
{
    INTCON = 0;     /* disable interrupts */
    INTCON2 = 0xF5;
    INTCON3 = 0xC0;
    PIE1 = 0;
    PIE2 = 0;

    OSCCON = 0b01100000; /* Enter Sleep mode for sleep, */
                         /* set internal oscillator to 8MHz, */
                         /* use primary clock selected by config words */
    /* Turn off the PLL */
    OSCTUNEbits.PLLEN = 0;

    /* disable ADC inputs */
    ANSEL = 0;
    ANSELH = 0;

    /* disable Comparators */
    CM1CON0 = 0;
    CM2CON0 = 0;

    /* make all available GPIOs outputs and set low */
    LATA  = 0x00;
    TRISA = 0xC0; /* leave RA6,RA7 as inputs */
    LATB  = 0x00;
    TRISB = 0x00;
    LATC  = 0x00;
    TRISC = 0x03; /* leave RC0,RC1 as inputs */

    RCONbits.IPEN = 0; /* use legacy interrupt model */
}
/* 
 * Setup PWM time base for an 1000Hz period.
 * 
 * Note 1:  Duty cycle units
 * 
 *          The duty cycle is in a 10-bit register. With
 *          a resolution in time that is 4 time that of 
 *          the PWM period register (PR2). The high 8-bits
 *          of this register are in the CCPRxL register,
 *          the low 2-bits are in the CCPxCON<5:4> register.
 * 
 *          The general case math to compute a percent of 
 *          the PWM period to set the duty cycle is:
 *          DutyCycle = PwmPeriod * DutyCyclePercent / 100
 * 
 *          The specific case using integer math is:
 *          DutyCycle = (PR2+1) * 4 * DutyCyclePercent / 100
 * 
 *          Combine terms to simplify and limit range to a 16-bit interger:
 *          DutyCycle = (PR2+1) * DutyCyclePercent / 25
 * 
 * WARNING: PMW1 and PWM2 share TIMER2 as the PWM time base.
 * When using both PWM function blocks in the PIC18F26K20
 * both must use the same time base period.
 *
 */ 
#define PWM_IF PIR1bits.TMR2IF
#define PWM_CYCLES_PER_SECOND (1000L)
#define TMR2_PRESCALE_SETTING (2) /* value can be 0, 1 or 2) sets prescale to 1:1, 4:1 or 16:1 */
#define PWM_PERIOD (FCYC/(PWM_CYCLES_PER_SECOND * (1 << (2*TMR2_PRESCALE_SETTING))))
#if (PWM_PERIOD > 256)
#error PWM_CYCLES_PER_SECOND too slow for TIMER2 prescale
#elif (PWM_PERIOD <= 1)
#error PWM_CYCLES_PER_SECOND too fast for TIMER2 prescale
#endif
void PWM_TimeBase_Init(void)
{ 
    T2CON = 0; /* stop TIMER2 */
    CCP1CON = 0; /* stop PWM1 */
    CCP2CON = 0; /* stop PWM2 */
    TRISCbits.TRISC2 = 1; /* make CCP1 tri-state */
    TRISCbits.TRISC1 = 1; /* make CCP2 tri-state */

    PR2 = PWM_PERIOD - 1; /* set PWM1 period */
    T2CON = TMR2_PRESCALE_SETTING;
    T2CONbits.TMR2ON = 1; /* start PWM1 timer */
}
/* 
 * Setup PWM1 for a 70% duty cycle.
 *
 * WARNING: PMW1 and PWM2 share TIMER2 as the PWM time base.
 * When using both PWM function blocks in the PIC18F26K20
 * both must use the same time base period.
 *
 */ 
void PWM1_Init(void)
{ 
    uint16_t DutyCycle;

    TRISCbits.TRISC2 = 1; /* make CCP1 tri-state */
    ECCP1AS = 0; /* disable auto shutdown */
    CCP1CONbits.P1M = 0b00; /* set PWM1 for single output */

    /* set duty cycle to 70%  */
    DutyCycle = ((uint16_t)(PR2+1)*70)/25; /* See: Note 1: Duty cycle units */

    CCP1CONbits.DC1B =  DutyCycle & 0b11;
    CCPR1L = (unsigned char)(DutyCycle >> 2);

    CCP1CONbits.CCP1M = 0b1100; /* set PWM1 mode */

    PWM_IF = 0;
    while(!PWM_IF); /* wait for PWM1 to complete first cycle */

    /* enable the PWM1 output */
    TRISCbits.TRISC2 = 0;
} 
/* 
 * Setup PWM2 for a 30% duty cycle.
 *
 * WARNING: PMW1 and PWM2 share TIMER2 as the PWM time base.
 * When using both PWM function blocks in the PIC18F26K20
 * both must use the same time base period.
 *
 */ 
void PWM2_Init(void)
{ 
    uint16_t DutyCycle;

    TRISCbits.TRISC1 = 1; /* make CCP2 tri-state */

    /* set duty cycle to 30%  */
    DutyCycle = ((uint16_t)(PR2+1)*30)/25; /* See: Note 1: Duty cycle units */

    CCP2CONbits.DC2B =  DutyCycle & 0b11;
    CCPR2L = (unsigned char)(DutyCycle >> 2);

    CCP2CONbits.CCP2M = 0b1100; /* set PWM2 mode */

    T2CONbits.TMR2ON = 1; /* start PWM2 timer */

    PWM_IF = 0;
    while(!PWM_IF); /* wait for PWM2 to complete first cycle */

    /* enable the PWM2 output */
    TRISCbits.TRISC1 = 0;
} 
/*
 * Main application 
 */
void main(void) 
{ 
    Init_PIC();
    PWM_TimeBase_Init();
    PWM1_Init();
    PWM2_Init();
    /* 
     * Application loop 
     */
    for(;;)
    {
        PWM_IF = 0;
        while(!PWM_IF);
    }
}