#include <reg52.h>
void Delay(unsigned int i)//延時
{
while(i--);
}


main()
{
    unsigned int a,j,k,n,m;
    n=500;
    k=n/3;
    m=3;
    while(1)
    {
    for(a=0;a<k;a++)
    {
        for(j=0;j<m;j++)
        {
        P0=0x00;
        Delay (a);
        P0=0xFF;
        Delay ((k-a));
        }
    }
    for(a=0;a<k;a++)
    {
        for(j=0;j<m;j++)
        {
        P0=0xFF;
        Delay (a);
        P0=0x00;
        Delay ((k-a));
        }
    }
    }
}