BugWorkShop - 甲蟲工作室: DIY - PIC：PIC18F4550 PWM 可調整佔空比程式 (五十六)

DIY - PIC：PIC18F4550 PWM 可調整佔空比程式 (五十六) ：

Microchip PIC18F4550 PWM 可調整佔空比程式是利用一個可變電阻來調節， PWM 的佔空比更會改變，佔空比可以調節從 0% 至 100% (理想值) 。可變電阻器 (10KΩ)是連接到類比數位轉換器 (A/D) 引腳，調節可變電阻器的電阻值，從而改變電壓輸入到類比數位轉換器，類比數位轉換器便將電壓轉化為數值，數值會換算為百份比，這個百份比便是佔空比的數值，佔空比的數值計算計出 CCPRxL: CCPxCON<5:4>的週期數值，便可更改 PWM 的佔空比。

▲ PIC18F4550 PWM 可調整佔空比程式流程圖

主程式：

void main(void)
{

    // LCD Display         1234567890123456
    char LCD_name[] ="BWS PWM>>(DC) v1";
    char LCD_name2[]="                ";

    // Local Variables

    // Variables for ADC
    float adc0_volt;
    unsigned int adc0_dec;
    unsigned int adc0_100;
    unsigned int adc0_volt1;
    unsigned int adc0_volt2;
    unsigned int float_base=1000;

    // Initialise Port
    TRISA = 0b00000001;                 // Setup RA0=Input RA1=Output
    TRISB = 0b11100000;                 // Set PORTB RB5 as Key In
    TRISC = 0b11111001;                 // Set PORTC C1 and C2 as PWM output
    LATC = 0b00000000 ;                // Clear PORTC

    // Initialise LCD
     OpenXLCD(FOUR_BIT&LINES_5X7);        // Init the LCD Display
    while(BusyXLCD());
    WriteCmdXLCD(BLINK_OFF & CURSOR_OFF );
    while(BusyXLCD());
    stdout = _H_USER;                // Redirect I/O to LCD
    LcdSetLine1();                        // Put cursor on start of line 1
    putsXLCD(LCD_name);         // Display text

    // Initialise ADC
    OpenADC(ADC_FOSC_32 &        // A/D clock source set to 32Tosc
            ADC_RIGHT_JUST &            // ADRESH:ADRESL from roght
            ADC_20_TAD,                        // A/D Acquisition time: 20TAD
            ADC_CH0 &                           // Analog Channel0 AN0
            ADC_INT_OFF &                // ADC Interrupt off
            ADC_VREFPLUS_VDD &    // Vref+ = VDD
            ADC_VREFMINUS_VSS,     // Vref- = VSS
            0b1110                          // ADCON0 = 7 = 00001110=AN0 Analog
             );

    //Configure CCP module as (PR2+1)*4*TOSC*T2_PS
    // PWM = 10kHz TMR_PS=1:4 Tosc=20MHz
    PR2     = 124;                           // PWM Frequency = 124 = 10kHz = 0.1ms
    T2CON   = 0b00000110 ;        // 11=1:16 10=1:4 00=1:1
    CCP1CON = 0b00001100 ;    // PWM Mode P1A/P1C/P1B/P1D=H <5:4> DC
    CCP2CON = 0b00111100 ;    // PWM Mode P2A/P2C/P2B/P2D=H
                                                     // Duty Cycle CCP1CON<5:4>+CCPR1L

    while(1)
    {
        ConvertADC();                     // Start an A/D Conversion
        while(BusyADC());               // Wait for Conversion Finished
        adc0_dec=ReadADC();       // Read A/D Result

        // Convert Floating Point to Decimal
        adc0_volt=(float)adc0_dec/1024*5; // 1024 Step and Vref=5V
        adc0_100 = adc0_dec/10.2;             // Calaculate Percentage %
        LcdSetLine2();                        // Put cursor on start of line 2
        printf("D=%04i=%0.3i%",adc0_dec,adc0_100);

        // CCPRxL:CCPxCON<5:4>*Tosc*TMR2_PS
        CCPR1L = ((PR2+1)*(adc0_100))/100;   // Calaculate Count of Duty Cycle
        printf("=%0.3i",CCPR1L);                         // Display CCPR1L
    } // End While
}