1.4 Getting Started with PWM

To generate this project using MPLAB® Code Configurator (MCC), follow the next steps:

1. Create a new MPLAB X IDE project for PIC18F47Q10.
2. Open the MCC from the toolbar. Information about how to install the MCC plug-in can be found here.
3. Go to Project Resources → System → System Module and do the following configuration:
   • Oscillator Select: LFINTOSC
   • Clock Divider: 1
   • In the Watchdog Timer Enable field from the WWDT tab, make sure WDT Disabled is selected.
   • In the Programming tab, make sure Low-Voltage Programming Enable is checked.
4. From the Device Resources window, add TMR2 and CCP1. Do the following configurations for each peripheral:

   Timer2 Configuration:

   • Hardware Settings tab
     • Enable Timer: checked
     • Control Mode: Roll over pulse
     • Start/Reset Option: Software control
   • Timer Clock tab
     • Clock Source: F_OSC/4
     • Prescaler: 1:32
     • Postscaler: 1:1
   • Timer Period tab
     • Timer Period: 1.057s
   • Software Settings tab
     • Enable Timer Interrupt: unchecked

   CCP1 Configuration:

   • Enable CCP: checked
   • CCP Mode: PWM
   • Select Timer: Timer2
   • Duty Cycle: 25%
   • CCPR Alignment: right_aligned
5. Open Pin Manager → Grid View window, select UQFN40 in the Package field and do the following pin configurations:
   • Set Port B pin 4 (RB4) as output for CCP1
   • Set Port E pin 2 (RE2) as GPIO input

   

6. Go to Project Resources → System → Pin Module → Easy Setup and enable WPU for the RE2 pin.
7. Click Generate in the Project Resources tab.
8. In the main.c file generated by MCC, add the following code:
   • ButtonCheck() function
   • Button press handling

   The ButtonCheck() function is used to detect if the button is pressed and, if so, to differentiate a long button press from a short button press. The method used is the incrementation of a counter. As long as the button is pressed, the counter value increments continuously and, after that, a check is performed to determine if the counter value is smaller or greater than a specific threshold. The function can return one of the three states: BT_NOCHANGE, BT_SHORT_PRESS, BT_LONG_PRESS.

   The button press handling is done inside the while(1) loop. The ButtonCheck() function is called continuously and, depending on the value that it returned, the PWM frequency and duty cycle change, as referenced earlier in this use case.

The necessary code and functions to implement the presented example are analyzed in this section.

The first step is to configure the microcontroller to disable the Watchdog Timer and to enable Low-Voltage Programming.

#pragma config WDTE = OFF
#pragma config LVP = ON 

The internal oscillator must be set to the desired value. Since the purpose of this example is to generate a low-speed PWM signal, the Low-Frequency Oscillator was used. The value of the clock frequency will be 31 kHz. This translates into the following function:

static void CLK_Initialize(void)
{
    /* Configure NOSC LFINTOSC; NDIV 1 FOSC = 31kHz */
    OSCCON1bits.NOSC = 5;
    OSCCON1bits.NDIV = 0;
}

The output driver for I/O pin RB4 must be enabled since it will be used as CCP1 output while RE2 must be configured as analog input with internal pull-up enabled. This translates into the following function:

static void PORT_Initialize(void)
{
    /* RB4 is output for PWM1 */
    TRISBbits.TRISB4 = 0;
    /* RE2 is digital input with pull-up for push-button */
    TRISEbits.TRISE2 = 1;
    ANSELEbits.ANSELE2 = 0;
    WPUEbits.WPUE2 = 1;
}   

For Timer2 to use as clock source F_OSC/4 with a 1:32 clock prescaler, the following function is used:

#define _XTAL_FREQ                      31000UL

#define FREQUENCY_MIN                   1    /* Hz */
#define TIMER_PRESCALER                 32   /* 1:32 */
#define FREQUENCY_TO_PR_CONVERT(F)      (uint8_t)(((_XTAL_FREQ)/ \
                                        (4*(F))/(TIMER_PRESCALER))-1)
static void TMR2_Initialize(void)
{
    /* TIMER2 clock source is FOSC/4 */
    T2CLKCONbits.CS = 1;

    /* TIMER2 counter reset */
    T2TMR = 0x00;

    /* TIMER2 ON, prescaler 1:32, postscaler 1:1 */
    T2CONbits.OUTPS = 0;
    T2CONbits.CKPS = 5;
    T2CONbits.ON = 1;

    /* Configure the default period */
    PR2 = FREQUENCY_TO_PR_CONVERT(FREQUENCY_MIN);
}

CCP1 is configured in PWM mode and uses Timer2 as period generator. The value from the CCPR1 register is left-aligned and the initial duty cycle value is set at 25%. This translates into the following function:

#define _XTAL_FREQ                       31000UL

#define FREQUENCY_MIN                    1   /* Hz */
#define DUTYCYCLE_MIN                    25  /* percents */

#define DUTYCYCLE_TO_CCPR_CONVERT(D,F)  (uint16_t)((float)(D)*(((_XTAL_FREQ)/ \
                                        (F)/(TIMER_PRESCALER))-1)/100.0)

static void PWM1_Initialize(void)
{
	/* MODE PWM; EN enabled; FMT left_aligned */
    CCP1CONbits.MODE = 0x0C;
    CCP1CONbits.FMT = 1;
    CCP1CONbits.EN = 1;

	/* Selecting Timer 2 */
    CCPTMRSbits.C1TSEL = 1;

    /* Configure the default duty cycle */
    CCPR1 = (DUTYCYCLE_TO_CCPR_CONVERT(DUTYCYCLE_MIN, FREQUENCY_MIN)) << 6;
}

Configuring the location of the pins is independent of the application purpose and the CCP mode. Each microcontroller has its own default physical pin position for peripherals, though the pin positions can be changed using the Peripheral Pin Select (PPS).

Therefore, the CCP pins can be relocated using the CCP1PPS and CCP2PPS registers for the input channels while using the RxyPPS registers for the output channels. The PPS configuration values can be found in the Peripheral Pin Select Module section of a device data sheet. For this example, the output PWM signal from CCP1 will be routed to the RB4 pin. This translates into the following code:

static void PPS_Initialize(void)
{
    /* Configure RB4 for PWM1 output */
    RB4PPS = 0x05;
}

At run time, the PWM generator is configured using these functions for duty cycle and period values respectively:

static   void PWM1_LoadDutyValue(uint16_t dutyValue)
{
    /* Only the upper 10 bits are used in register CCPR1 */
    CCPR1 = dutyValue << 6;
}

static  void TMR2_LoadPeriodRegister(uint8_t periodVal)
{
    /* Configure the period register */
    PR2 = periodVal;
}

The ButtonCheck() function is used to detect if the button is pressed and, if so, to differentiate a long button press from a short button press. The method used is the incrementation of a counter. As long as the button is pressed, the counter value increments continuously and, after that, a check is performed to determine if the counter value is smaller or greater than a specific threshold. The function can return one of the three states: BT_NOCHANGE, BT_SHORT_PRESS, BT_LONG_PRESS.

The button press handling is done inside the while(1) loop. The ButtonCheck() function is called continuously and, depending on the value that it returned, the PWM frequency and duty cycle changes, as referenced earlier in this use case.

To generate this project using MPLAB® Code Configurator (MCC), follow the next steps:

1. Create a new MPLAB X IDE project for PIC18F47Q10.
2. Open the MCC from the toolbar. Information about how to install the MCC plug-in can be found here.
3. Go to Project Resources → System → System Module and do the following configuration:
   • Oscillator Select: HFINTOSC
   • HF Internal Clock: 64_MHz
   • Clock Divider: 1
   • In the Watchdog Timer Enable field in the WWDT tab, make sure WDT Disabled is selected.
   • In the Programming tab, make sure Low-Voltage Programming Enable is checked.
4. From the Device Resources window, add TMR4 and CCP2. Do the following configurations for each peripheral:

   Timer4 Configuration:

   • Hardware Settings tab
     • Enable Timer: checked
     • Control Mode: Roll over pulse
     • Start/Reset Option: Software control
   • Timer Clock tab
     • Clock Source: F_OSC/4
     • Prescaler: 1:2
     • Postscaler: 1:1
   • Timer Period tab
     • Timer Period: 20 us
   • Software Settings tab
     • Enable Timer Interrupt: unchecked

   CCP2 Configuration:

   • Enable CCP: checked
   • CCP Mode: PWM
   • Select Timer: Timer4
   • Duty Cycle: 5%
   • CCPR Alignment: right_aligned
5. Open Pin Manager → Grid View window, select UQFN40 in the Package field and do the following pin configurations:
   • Set Port C pin 7 (RC7) as output for CCP2
   • Set Port E pin 2 (RE2) as GPIO input

   

6. Go to Project Resources → System → Pin Module → Easy Setup and enable WPU for the RE2 pin.
7. Click Generate in the Project Resources tab.
8. In the main.c file generated by MCC, add the following code:
   • ButtonCheck() function
   • Button press handling

   The ButtonCheck() function is used to detect if the button is pressed. Whenever a press is detected, a 10 ms delay is applied to avoid the bouncing effect and the program waits until the button is released. The function can return one of the two states: BT_NOCHANGE or BT_PRESS.

   void main(void)
   {
       uint8_t index = 0;
       /*  Initialize the device */
       SYSTEM_Initialize();
   
       while (1)
       {
           if(ButtonCheck() == BT_PRESS)
           {
               /* When a button press is detected, the index is updated */
               index++;
               if(index >= FREQUENCY_LIST_DIMENSION)
                   index = 0;
   
               /* and the frequency is changed to the next one in the list */
               TMR4_LoadPeriodRegister(frequencies_list[index]);
           }        
       }
   }

   The frequencies_list array contains the selectable PWM frequencies presented in the description of this use case (50 kHz, 100 kHz, 200 kHz, 400 kHz, and 800 kHz).

The necessary code and functions to implement the presented example are analyzed in this section.

The first step is to configure the microcontroller to disable the Watchdog Timer and to enable Low-Voltage Programming.

#pragma config WDTE = OFF
#pragma config LVP = ON

The internal oscillator must be set to the desired value. This example uses the HFINTOSC with a frequency of 64 MHz. This translates into the following function:

static void CLK_Initialize(void)
{
    /* Configure NOSC HFINTOSC; NDIV 1; FOSC = 64MHz */
    OSCCON1bits.NOSC = 6;
    OSCCON1bits.NDIV = 0;

    /* HFFRQ 64_MHz */
    OSCFRQbits.HFFRQ = 8;
}

The output driver for I/O pin RC7 must be enabled since it will be used as CCP2 output. RE2 must be configured as analog input with internal pull-up enabled. This translates into the following function:

static void PORT_Initialize(void)
{
    /* RC7 is output for PWM2 */
    TRISCbits.TRISC7 = 0;
    /* RE2 is digital input with pull-up for push-button */
    TRISEbits.TRISE2 = 1;
    ANSELEbits.ANSELE2 = 0;
    WPUEbits.WPUE2 = 1;
}

For Timer4 to use as clock source F_OSC/4 with a 1:2 clock prescaler, the following function is used:

static void TMR4_Initialize(void)
{
    /* TIMER4 clock source is FOSC/4 */
    T4CLKCONbits.CS = 1;

    /* TIMER4 counter reset */
    T4TMR = 0x00;

    /* TIMER4 ON, prescaler 1:2, postscaler 1:1 */
    T4CONbits.OUTPS = 0;
    T4CONbits.CKPS = 1;
    T4CONbits.ON = 1;

    /* Configure initial period register value */
    PR4 = frequencies_list[0];
}

CCP2 is configured in PWM mode with a constant pulse-width of one microsecond and uses Timer4 as period generator. This translates into the following function:

static void PWM2_Initialize(void)
{
    /* MODE PWM; EN enabled; FMT right_aligned */
    CCP2CONbits.MODE = 0x0C;
    CCP2CONbits.FMT = 0;
    CCP2CONbits.EN = 1;

    /* Constant on-time setting is 1 us */
    CCPR2 = 32;
    
    /* Select timer 4 */
    CCPTMRSbits.C2TSEL = 2;
}

Configuring the location of the pins is independent of the application purpose and the CCP mode. Each microcontroller has its own default physical pin position for peripherals, but the pin positions can be changed using the Peripheral Pin Select (PPS).

Therefore, the CCP pins can be relocated using the CCP1PPS and CCP2PPS registers for the input channels while using the RxyPPS registers for the output channels.

The PPS configuration values can be found in the Peripheral Pin Select Module section of a device data sheet. For this example, the output PWM signal from CCP2 will be routed to RC7 pin. This translates into the following code:

static void PPS_Initialize(void)
{
    /* Configure RC7 for PWM2 output */
    RC7PPS = 0x06;
}

The ButtonCheck() function is used to detect if the button is pressed. Whenever a press is detected, a delay of 10 ms is applied to avoid the bouncing effect and the program waits until the button is released. The function can return one of the two states: BT_NOCHANGE or BT_PRESS.

static void TMR4_LoadPeriodRegister(uint8_t periodVal)
{
    /* Configure the period register */
    PR4 = periodVal;
}

void main(void)
{
    uint8_t index = 0;
    /*  Initialize the device */
    PORT_Initialize();
    PPS_Initialize();
    CLK_Initialize();
    TMR4_Initialize();
    PWM2_Initialize();

    while (1)
    {
        if(ButtonCheck() == BT_PRESS)
        {
            /* When a button press is detected, the index is updated */
            index++;
            if(index >= FREQUENCY_LIST_DIMENSION)
                index = 0;

            /* and the frequency is changed to the next one in the list */
            TMR4_LoadPeriodRegister(frequencies_list[index]);
        }        
    }
}

The frequencies_list array contains the selectable PWM frequencies presented in the description of this use case (50 kHz, 100 kHz, 200 kHz, 400 kHz and 800 kHz).

To generate this project using MPLAB® Code Configurator (MCC), follow the next steps:

1. Create a new MPLAB X IDE project for PIC18F47Q10.
2. Open the MCC from the toolbar. Information about how to install the MCC plug-in can be found here.
3. Go to Project Resources → System → System Module and do the following configuration:
   • Oscillator Select: HFINTOSC
   • HF Internal Clock: 64_MHz
   • Clock Divider: 1
   • In the Watchdog Timer Enable field in the WWDT tab, make sure WDT Disabled is selected.
   • In the Programming tab, make sure Low-Voltage Programming Enable is checked.
4. From the Device Resources window, add TMR2, CCP1, CCP2 and PWM3. Do the following configurations for each peripheral:

   Timer2 Configuration:

   • Hardware Settings tab
     • Enable Timer: checked
     • Control Mode: Roll over pulse
     • Start/Reset Option: Software control
   • Timer Clock tab
     • Clock Source: F_OSC/4
     • Prescaler: 1:8
     • Postscaler: 1:16
   • Timer Period tab
     • Timer Period: 2.048 ms
   • Software Settings tab
     • Enable Timer Interrupt: checked

   CCP1 Configuration:

   • Enable CCP: checked
   • CCP Mode: PWM
   • Select Timer: Timer2
   • Duty Cycle: 100.0%
   • CCPR Alignment: left_aligned

   CCP2 Configuration:

   • Enable CCP: checked
   • CCP Mode: PWM
   • Select Timer: Timer2
   • Duty Cycle: 100.0%
   • CCPR Alignment: left_aligned

   PWM3 Configuration:

   • Enable CCP: checked
   • Select Timer: Timer2
   • Duty Cycle: 100.0%
   • PWM Polarity: active_hi
5. Open Pin Manager → Grid View window, select UQFN40 in the Package field and do the following pin configurations:
   • Set Port B pin 0 (RB0) as output for CCP1
   • Set Port B pin 3 (RB3) as output for CCP2
   • Set Port D pin 0 (PD0) as output for PWM3

   

6. Go to Project Resources → System → Pin Module → Easy Setup and enable WPU for the RE2 pin.
7. Click Generate in the Project Resources tab.
8. In the main.c file generated by MCC, add the following code:
   • Enable the global interrupt function
   • Add TMR2 interrupt function
   • Set the TMR2 interrupt handler initializer

   void RGB_LED_Handler(void);
   
   void main(void)
   {
       /* Initialize the device */
       SYSTEM_Initialize();
       TMR2_SetInterruptHandler(RGB_LED_Handler);
   
       /* Enable the Global Interrupts */
       INTERRUPT_GlobalInterruptEnable();
   
       /* Enable the Peripheral Interrupts */
       INTERRUPT_PeripheralInterruptEnable();
   
       while (1)
       {
           //Add your application code
       }
   }
   

   The RGB_LED_Handler() function creates the color game on the RGB LED, as presented in the description of this use case.

   

The necessary code and functions to implement the presented example are analyzed in this section.

The first step is to configure the microcontroller to disable the Watchdog Timer and to enable Low-Voltage Programming.

#pragma config WDTE = OFF
#pragma config LVP = ON

The internal oscillator must be set to the desired value. This example uses the HFINTOSC with a frequency of 64 MHz. This translates into the following function:

static void CLK_Initialize(void)
{
    /* Configure NOSC HFINTOSC; NDIV 1; FOSC = 64MHz */
    OSCCON1bits.NOSC = 6;
    OSCCON1bits.NDIV = 0;

    /* HFFRQ 64_MHz */
    OSCFRQbits.HFFRQ = 8;
}

The output driver for I/O pins RB0, RB3 and RD0 must be enabled. They will be used as output for CCP1, CCP2 and PWM3, respectively. This translates into the following function:

static void PORT_Initialize(void)
{
    /* RB0 is output for PWM1 */
    TRISBbits.TRISB0 = 0;
    /* RB3 is output for PWM2 */
    TRISBbits.TRISB3 = 0;
    /* RD0 is output for PWM3 */
    TRISDbits.TRISD0 = 0;
}

Timer2 uses as clock source F_OSC/4 with a 1:8 clock prescaler and a 1:16 postscaler and has the overflow interrupt enabled. This translates into the following function:

#define MAX_DCY                1023

static void TMR2_Initialize(void)
{
    /* TIMER2 clock source is FOSC/4 */
    T2CLKCONbits.CS = 1;

    /* TIMER2 counter reset */
    T2TMR = 0x00;

    /* TIMER2 prescaler 1:8, postscaler 1:16 */
    T2CONbits.CKPS = 3;
    T2CONbits.OUTPS = 15;

    /* TIMER2 period register setting, divided by 4 because FOSC/4 is used for PWM mode */
    T2PR = MAX_DCY >> 2;

    /* Clearing IF flag before enabling the interrupt */
    PIR4bits.TMR2IF = 0;

    /* Enabling TIMER2 interrupt */
    PIE4bits.TMR2IE = 1;

    /* TIMER2 ON */
    T2CONbits.ON = 1;
}

CCP1 is configured in PWM mode and uses Timer2 as period generator. The value from the CCPR1 register is left-aligned and the initial duty cycle value is set at 100%, corresponding to a minimum brightness in common anode LEDs. For a common cathode LED, the initial duty cycle will be set at 0%. This translates into the following function:

#define MAX_DCY                       1023
#define LED_MIN_BRIGHT                (MAX_DCY)

static void PWM1_Initialize(void)
{
    /* MODE PWM; EN enabled; FMT left_aligned */
    CCP1CONbits.MODE = 0x0C;
    CCP1CONbits.FMT = 1;
    CCP1CONbits.EN = 1;

    /* Selecting Timer 2 */
    CCPTMRSbits.C1TSEL = 1;
    
    /* Configure initial duty cycle */
    CCPR1 = (uint16_t)LED_MIN_BRIGHT << 6;
}

CCP2 is configured in PWM mode and uses Timer2 as period generator. The value from the CCPR2 register is left-aligned and the initial duty cycle value is set at 100%, corresponding to a minimum brightness in common anode LEDs. For a common cathode LED, the initial duty cycle will be set at 0%. This translates into the following function:

#define MAX_DCY                       1023
#define LED_MIN_BRIGHT                (MAX_DCY)

static void PWM2_Initialize(void)
{
    /* MODE PWM; EN enabled; FMT left_aligned */
    CCP2CONbits.MODE = 0x0C;
    CCP2CONbits.FMT = 1;
    CCP2CONbits.EN = 1;

    /* Selecting Timer 2 */
    CCPTMRSbits.C2TSEL = 1;

    /* Configure initial duty cycle */
    CCPR2 = (uint16_t)LED_MIN_BRIGHT << 6;
}

PWM3 uses Timer2 as period generator. The initial duty cycle value is set at 100%, corresponding to a minimum brightness in common anode LEDs. For a common cathode LED, the initial duty cycle will be set at 0%. This translates into the following function:

#define MAX_DCY                       1023
#define LED_MIN_BRIGHT                (MAX_DCY)

static void PWM3_Initialize(void)
{
    /* PWM3 enabled module, polarity normal */
    PWM3CONbits.EN = 1;
    PWM3CONbits.POL = 0;

    /* Select timer 2 */
    CCPTMRSbits.P3TSEL = 1;

    /* Configure initial duty cycle */
    PWM3DC = (uint16_t)LED_MIN_BRIGHT << 6;
}

Configuring the location of the pins is independent of the application purpose and the CCP mode. Each microcontroller has its own default physical pin position for peripherals, but the pin positions can be changed using the Peripheral Pin Select (PPS).

Therefore, the CCP pins can be relocated using the CCP1PPS and CCP2PPS registers for the input channels while using the RxyPPS registers for the output channels. The PPS configuration values can be found in the Peripheral Pin Select Module section of a device data sheet.

For this example, the output PWM signal from CCP1 will be routed to the RB0 pin, the output PWM signal from CCP2 will be routed to RB3, and the output PWM signal from PWM3 will be routed to RD0. This translates into the following code:

static void PPS_Initialize(void)
{
    /* Configure RB0 for PWM1 output */
    RB0PPS = 0x05;
    /* Configure RB3 for PWM2 output */
    RB3PPS = 0x06;
    /* Configure RD0 for PWM3 output */
    RD0PPS = 0x07;
}

Before any processing is done, the interrupts of the microcontroller must be activated. This is done by setting the Global Interrupt Enable (GIE) and the Peripheral Interrupt Enable (PIE) bits of the INTCON register.

static void  INTERRUPT_Initialize(void)
{
    /* Enable the Global Interrupts */
    INTCONbits.GIE = 1;

    /* Enable the Peripheral Interrupts */
    INTCONbits.PEIE = 1;
}

Whenever Timer2 interrupt occurs, the duty cycle of the PWM signals is changed as mentioned in the use case description.

static void TMR2_ISR(void)
{
    /* clear the TMR2 interrupt flag */
    PIR4bits.TMR2IF = 0;
    
    /* user ISR function call; */
    RGB_LED_Handler();
}

The RGB_LED_Handler() function creates the color game on the RGB LED, as presented in the use case description. Using LED_COMMON_ANODE macro definition, the color sequence can be configured at compile time for either common anode or common cathode LEDs.

The Timer2 interrupt handler is handled by the following function:

static void __interrupt() INTERRUPT_InterruptManager (void)
{
    /* interrupt handler */
    if(INTCONbits.PEIE)
    {
        if( (PIE4bits.TMR2IE) && (PIR4bits.TMR2IF) )
        {
            TMR2_ISR();
        }
    }
}