利用定时器产生500Hz方波

#include <reg51.h>
sbit POUT = P2 ^ 1;
void main(void)
{
    TMOD = 0x01;
    TH0 = 0xfc;
    TL0    = 0x18;
    TR0 = 1;
    while(1)
    {
        if( TF0 == 1)                                        
        {
            TF0 = 0 ;
            TH0 = 0xfc;
            TL0 = 0x18;
            POUT = !POUT;
        }
    }
}