如下程序目的为控制一C51单片机通过其P0口，实现LED灯周

#include<reg51.h>
    int main(void)
    {
        unsigned char counter
        TMOD=0x01;
        TH0=(65536-46083)/256;
        TL0=(65536-46083)%256;
        TF0=0;
        P0=0xff;
        counter=0;
        TR0=1;
        while(1)
        {
            while(TF0==1)
            {
                counter++;
                if(counter==20)
                {
                    __________
                    counter=0;
                }
                TH0=(65536-46083)/256;
                TL0=(65536-46083)%256;
            }
        }
    }