PWM（脈寬調製）大家可以上網查查，其原理講解很多。為了更好的學習PWM，我特意參照別人寫的文章，自己也寫了一份程式碼來實現PWM。程式碼如下：

#include <stc12c5a60s2.h>

unsigned long cnt;
unsigned int cnt_T1;
unsigned int high;
unsigned int low;
unsigned char TH0_high;
unsigned char TL0_high;
unsigned char TH0_low;
unsigned char TL0_low;
unsigned char T1H1;
unsigned char T1L1;
unsigned char flag=0;

unsigned char duty[19] = {5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85,90,95};
unsigned char index=0;

void config_Fy_and_dy(unsigned char fy, unsigned char dy);
void config_Timer1(unsigned char ms);
void modify_duty(unsigned char dy);

sbit PWM_OUT = P2^5;

void main()
{
    TMOD = 0X11;    //  定時器0/1都工作在方式1，是2^16計數
    EA=1;
    config_Fy_and_dy(100, 20);
    config_Timer1(50);
    while(1);
}

void config_Fy_and_dy(unsigned char fy, unsigned char dy) // 輸入頻率fy，佔空比dy 
{
    cnt =  (11059200/fy)/12;    //  要產生頻率為fy，定時器0所要計的數值
    high = (cnt*dy)/100;        //  計算出高電平所要計的數值
    low = cnt - high;   //  計算出低電平所要計的數值
    high = 65536 - high;  //  確定定時器0，從哪個初值開始計時，記錄的是高電平
    low = 65536 - low;  //  確定定時器0，從哪個初值開始計時，記錄的是低電平
    TH0_high = (unsigned char)(high>>8);    //  高電平，給TH0預備重灌初值
    TL0_high = (unsigned char)high;         //  高電平，給TL0預備重灌初值
    TH0_low = (unsigned char)(low>>8);      //  低電平，給TH0預備重灌初值
    TL0_low = (unsigned char)low;           //  低電平，給TL0預備重灌初值
    TH0 = TH0_high; 
    TL0 = TL0_high;
    PWM_OUT = 1;               
    ET0 = 1;
    TR0 = 1;
}

void config_Timer1(unsigned char ms)
{
    unsigned long temp;
    temp =  11059200/1000;
    temp = (temp*ms)/12;
    cnt_T1 = 65536 - temp;
    T1H1 = (unsigned char)(cnt_T1>>8);
    T1L1 = (unsigned char)cnt_T1;
    TH1 = T1H1;
    TL1 = T1L1;
    ET1=1;
    TR1=1;
}

void modify_duty(unsigned char dy)
{
    high = (cnt*dy)/100;
    low = cnt - high;
    high = 65536 - high;
    low  = 65536 - low;
    TH0_high = (unsigned char)(high>>8);    //  高電平，給TH0預備重灌初值
    TL0_high = (unsigned char)high;         //  高電平，給TL0預備重灌初值
    TH0_low = (unsigned char)(low>>8);      //  低電平，給TH0預備重灌初值
    TL0_low = (unsigned char)low;           //  低電平，給TL0預備重灌初值
}

void T0_Timer0() interrupt 1
{
    if(PWM_OUT==0)  //  準備產生高電平
    {
        TH0 = TH0_high;         //  高電平產生  初值重灌
        TL0 = TL0_high;
        PWM_OUT = 1;
    }
    else
    {
        TH0 = TH0_low;         //  低電平產生  初值重灌
        TL0 = TL0_low;
        PWM_OUT = 0;
    }
}

void T1_Timer1() interrupt 3
{
    TH1 = T1H1;
    TL1 = T1L1;
    modify_duty(duty[index]);
    if(0 == flag)   //  flag=0時，表示呼吸燈由暗變亮
    {
        index++;
        if(index >=18)
        {
            flag = 1;
        }
    }
    else
    {
        index--;
        if(index <=0)
        {
            flag=0;
        }
    }
}
 

其實，PWM這種實現方法並不適合程式設計，因為它佔用了兩個定時器中斷口，會影響程式的執行效率。

我是通過兩個定時器來更好的掌握PWM的調製原理。

接下來，我將會通過微控制器（STC12C5A60S2）內部模組實現PWM，實現比較簡單，將在下個文章來完成。