蜂鸣器的一点没想到

#include <reg52.h>

sbit BUZZ = P1^6;

unsigned char T0RH;
unsigned char T0RL;

void OpenBuzz(unsigned int fre);
void StopBuzz();

void main()
{
    unsigned int i;
    EA = 1;

    while(1)
    {
        OpenBuzz(4000);
        for(i=0; i<30000; i++);
        StopBuzz();
        for(i=0; i<30000; i++);
        OpenBuzz(1000);
        for(i=0; i<30000; i++);
        StopBuzz();
    }
}

void StopBuzz()
{
    ET0 = 0;
    TR0 = 0;
}

void OpenBuzz(unsigned int fre)
{
    unsigned int reload;

    reload = 65536 - (11059200)/(fre*2);
    T0RH = (unsigned char)(reload >> 8);
    T0RL = (unsigned char)reload;
    TMOD = 0x01;
    TH0 = 0xFF;
    TL0 = 0xFE;
    ET0 = 1;
    TR0 = 1;
}

void InterruptTimer0() interrupt 1
{
    TH0 = T0RH;
    TL0 = T0RL;

    BUZZ = ~BUZZ;
}

注意OpenBuzz里面的2，为什么要乘以2呢？ 注意，频率的定义为周期的倒数，是高低电平所占的整个周期。
但是本例子占空比直接默认的就是50，那么高电平所占的时间就是一半咯！