01第一節 知識點

（1）捕捉/ 比較/PWM （CCP）模塊

PIC18F2420/2520/4420/4520 器件配有兩個CCP （捕捉/ 比較/PWM）模塊。每個模塊包含一個16 位寄存器，它可以用作16 位捕捉寄存器、16 位比較寄存器或PWM 主/ 從占空比寄存器。

（2）PWM模式

在脈寬調制（Pulse Width Modulation，PWM）模式下，CCPx 引腳可輸出分辨率高達10 位的PWM輸出。由于CCP2 引腳與PORTB 或PORTC 數據鎖存器復用，因此必須清零相應的TRIS 位才能使CCP2 引腳成為輸出引腳。

（3） PWM周期

PWM 周期可以通過寫PR2 寄存器來指定。使用以下公式計算PWM 周期：

（4）PWM占空比

PWM 占空比可通過寫入CCPRxL 寄存器和CCPxCON5:4 位來指定。最高分辨率可達10 位。CCPRxL 包含占空比的高8 位，CCPxCON5:4 包含低2 位。由CCPRxL:CCPxCON5:4 表示這個10 位值。計算占空比的公式如下：

（5） PWM 模式設置

在為CCP 模塊配置PWM 工作模式時應該遵循以下步驟：

1）. 通過寫PR2 寄存器設置PWM 周期。

2）. 通過寫CCPRxL 寄存器和CCPxCON5:4 位來設置PWM 占空比。

3）. 通過清零相應的TRIS 位將CCPx 引腳配置為輸出。

4）. 通過寫T2CON 來設置TMR2 預分頻值并使能Timer2。

5）. 配置CCPx 模塊使之工作于PWM 模式。
（6）PWM相關的寄存器


（7）PWM的系統框圖

02程序設計

（1）pwm_config.h

/*
* File:  
* Author:
* Comments:
* Revision history:
*/


// This is a guard condition so that contents of this file are not included
// more than once. 
#ifndef _PWM_CONFIG_H_
#define           _PWM_CONFIG_H_


#include // include processor files - each processor file is guarded. 


void pwm_config_init(void);
unsignedint duty_percent(unsignedint per);
void pwm_config_duty(unsignedint duty);
#endif           /*  _PWM_CONFIG_H_ */

(2)pwm_config.c

/*
* File:   pwm_config.c
* Author: Greg Gong
*
* Created on July 4, 2018, 9:25 PM
*/
#include
#include "pwm_config.h"
#include "main.h"
#define  TIMER2PRE 16
#define PWM_freq   5000
/*
*pwm ccp1的設置，采用基本的pwm 模式，RC2 為pwm的輸出端口
* pwm的周期是2kHz， 占領比為 50%, 4kHz.
*/
void pwm_config_init(void)
{  
    CCP1CONbits.CCP1M=0b1111;// pwm mpdel.
    PR2=(_XTAL_FREQ/(PWM_freq*4*TIMER2PRE))-1;; // PWM 的周期為1/5kHz TMR2 預分頻為16
    TRISCbits.RC2=0; //output port
    T2CONbits.T2CKPS=0b11; //16分頻
    TMR2ON=1; //enable timer2

}
/*
* 占空比 10位 0~1023 對應 0%~100%
*
*
*/
void pwm_config_duty(unsignedint duty)
{   if(duty< < span="" >1023)
    {   duty = ((float)duty/1023)*(_XTAL_FREQ/(PWM_freq*TIMER2PRE));
      // CCPRXL和CCPCON< 5:4 >的轉空比
      CCP1CONbits.DC1B=0b11&duty;//0b00; //把pwm10位的低兩位賦值為< 5:4 >
      CCPR1L=duty >?>2;//0b1001110; // 高八位賦值為 CCPR1L
    }
}


unsignedint duty_percent(unsignedint per)
{
    return (unsignedint)(1023*per/100);

}

（3）main.c

/*
* File:   pwm_main.c
* Author: Greg Gong
*
* Created on 2021年2月28日, 下午11:07
*/
// PIC18F4520 Configuration Bit Settings


#pragma config OSC = HS         // Oscillator Selection bits (HS oscillator)
#pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
#pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover mode disabled)


// CONFIG2L
#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = SBORDIS  // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 3         // Brown Out Reset Voltage bits (Minimum setting)


// CONFIG2H
#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)


// CONFIG3H
#pragma config CCP2MX = PORTC   // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = OFF      // PORTB A/D Enable bit (PORTB< 4:0 >pins are configured as analog input channels on Reset)
#pragma config LPT1OSC = OFF    // Low-Power Timer1 Oscillator Enable bit (Timer1 configured for higher power operation)
#pragma config MCLRE = OFF      // MCLR Pin Enable bit (RE3 input pin enabled; MCLR disabled)


// CONFIG4L
#pragma config STVREN = OFF     // Stack Full/Underflow Reset Enable bit (Stack full/underflow will not cause Reset)
#pragma config LVP = OFF        // Single-Supply ICSP Enable bit (Single-Supply ICSP disabled)
#pragma config XINST = OFF      // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode disabled (Legacy mode))


// CONFIG5L
#pragma config CP0 = OFF        // Code Protection bit (Block 0 (000800-001FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (002000-003FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (004000-005FFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (006000-007FFFh) not code-protected)


// CONFIG5H
#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) not code-protected)
#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)


// CONFIG6L
#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (000800-001FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (002000-003FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (004000-005FFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (006000-007FFFh) not write-protected)


// CONFIG6H
#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)
#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot block (000000-0007FFh) not write-protected)
#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)


// CONFIG7L
#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (000800-001FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (002000-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (004000-005FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (006000-007FFFh) not protected from table reads executed in other blocks)


// CONFIG7H
#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot block (000000-0007FFh) not protected from table reads executed in other blocks)


// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.


#include
#include "pwm_config.h"
#include "main.h"
void main(void) {

    pwm_config_init();
    pwm_config_duty(duty_percent(50));
    return;
}

（4）main.h

/*
* File:  
* Author: Greg
* Comments:
* Revision history:
*/
// This is a guard condition so that contents of this file are not included
// more than once. 
#ifndef _MAIN_H_
#define _MAIN_H_
#include // include processor files - each processor file is guarded. 
#define _XTAL_FREQ 40000000 //定義時鐘為40MHz
#endif           /* XC_HEADER_TEMPLATE_H */

我們將代碼的占空比設置為100% 形式，下載到開發板可以看看效果。