51学习笔记之利用定时器0产生最大周期为16s的PWM波(STC12C5A60S2)

硬件：STC12C5A60S2 

功能：实现PWM波生成。该程序周期为256ms，输出端口为P1.3。

代码：

#include "reg51.h"
#include "intrins.h"
#define FOSC 11059260L
#define T1MS  (65536-FOSC/12/1000)

//定时器产生的脉冲大约为1MS，PWM经过256分频后的时间是256ms
//通过调T1MS的数值，PWM的最大周期时间是16s。

typedef unsigned char BYTE;
typedef unsigned int WORD;



/*Declare SFR associated with the PCA */
sfr CCON = 0xD8; //PCA control register
sbit CCF0 = CCON^0; //PCA module-0 interrupt flag
sbit CCF1 = CCON^1; //PCA module-1 interrupt flag
sbit CR = CCON^6; //PCA timer run control bit
sbit CF = CCON^7; //PCA timer overflow flag
sfr CMOD = 0xD9; //PCA mode register
sfr CL = 0xE9; //PCA base timer LOW
sfr CH = 0xF9; //PCA base timer HIGH
sfr CCAPM0 = 0xDA; //PCA module-0 mode register
sfr CCAP0L = 0xEA; //PCA module-0 capture register LOW
sfr CCAP0H = 0xFA; //PCA module-0 capture register HIGH
sfr CCAPM1 = 0xDB; //PCA module-1 mode register
sfr CCAP1L = 0xEB; //PCA module-1 capture register LOW
sfr CCAP1H = 0xFB; //PCA module-1 capture register HIGH
sfr PCAPWM0 = 0xf2;
sfr PCAPWM1 = 0xf3;

void Delay_xms(unsigned int z){        
    unsigned char i, j;
    unsigned int k;
    for(k=0;k<z;k++){            //
        _nop_();
        _nop_();
        i = 12;
        j = 84;
        do{while (--j);} 
        while (--i);
    }
    
}

//定时器0初始化

void Time0Init()
{
    TMOD = 0x01;
    TL0=T1MS;
    TH0=T1MS>>8;
    TR0=1;
    ET0=1;
    EA=1;    
}

void PWMInit()
{
    CCON = 0; //Initial PCA control register
    //PCA timer stop running
    //Clear CF flag
    //Clear all module interrupt flag
    CL = 0; //Reset PCA base timer
    CH = 0;
//    CMOD = 0x00; //Set PCA timer clock source as Fosc/2
    CMOD = 0x04;
    //Disable PCA timer overflow interrupt
    CCAP0H = CCAP0L = 0x80; //PWM0 port output 50% duty cycle square wave
    CCAPM0 = 0x42; //设备为定时器0溢出脉冲
    CCAP1H = CCAP1L = 0xff; //PWM1 port output 0% duty cycle square wave
    PCAPWM1 = 0x03;
    CCAPM1 = 0x42; //PCA module-1 work in 8-bit PWM mode
    //and no PCA interrupt
    CR = 1; //PCA timer start run
}



void PWMSet(float a)   //输入a表示占空比
{
    CCAP0H =CCAP0L =(BYTE)((1-a)*256);
}

void main()
{

    Time0Init();
  PWMInit();
    PWMSet(0.1);
while(1)
{

        PWMSet(0.5);    //占空比为百分之50
    Delay_xms(2000);
}
}


//定时器0中断
void tm0_isr() interrupt 1 using 1
{
    TL0=T1MS;
    TH0=T1MS>>8;
}