PWM（脉宽调制）大家可以上网查查，其原理讲解很多。为了更好的学习PWM，我特意参照别人写的文章，自己也写了一份代码来实现PWM。单片机代码如下：
- #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; // 定时器0/1都工作在方式1，是2^16计数
- EA=1;
- config_Fy_and_dy(100, 20);
- config_Timer1(50);
- while(1);
- }
-
- void config_Fy_and_dy(unsigned char fy, unsigned char dy) // 输入频率fy，占空比dy
- {
- cnt = (11059200/fy)/12; // 要产生频率为fy，定时器0所要计的数值
- high = (cnt*dy)/100; // 计算出高电平所要计的数值
- low = cnt - high; // 计算出低电平所要计的数值
- high = 65536 - high; // 确定定时器0，从哪个初值开始计时，记录的是高电平
- low = 65536 - low; // 确定定时器0，从哪个初值开始计时，记录的是低电平
- TH0_high = (unsigned char)(high>>8); // 高电平，给TH0预备重装初值
- TL0_high = (unsigned char)high; // 高电平，给TL0预备重装初值
- TH0_low = (unsigned char)(low>>8); // 低电平，给TH0预备重装初值
- TL0_low = (unsigned char)low; // 低电平，给TL0预备重装初值
- 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); // 高电平，给TH0预备重装初值
- TL0_high = (unsigned char)high; // 高电平，给TL0预备重装初值
- TH0_low = (unsigned char)(low>>8); // 低电平，给TH0预备重装初值
- TL0_low = (unsigned char)low; // 低电平，给TL0预备重装初值
- }
-
- void T0_Timer0() interrupt 1
- {
- if(PWM_OUT==0) // 准备产生高电平
- {
- TH0 = TH0_high; // 高电平产生 初值重装
- TL0 = TL0_high;
- PWM_OUT = 1;
- }
- else
- {
- TH0 = TH0_low; // 低电平产生 初值重装
- TL0 = TL0_low;
- PWM_OUT = 0;
- }
- }
-
- void T1_Timer1() interrupt 3
- {
- TH1 = T1H1;
- TL1 = T1L1;
- modify_duty(duty[index]);
- if(0 == flag) // flag=0时，表示呼吸灯由暗变亮
- {
- index++;
- if(index >=18)
- {
- flag = 1;
- }
- }
- else
- {
- index--;
- if(index <=0)
- {
- flag=0;
- }
- }
- }
其实，PWM这种实现方法并不适合编程，因为它占用了两个定时器中断口，会影响程序的执行效率。 我是通过两个定时器来更好的掌握PWM的调制原理。
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