#include<reg51.h>

sbit P0_0=P0^0;  //方波輸出端口


 timer1() interrupt 3 using 3  //定時(shí)中斷
 {  
   TL1=0xfe;            
   TH1=0xff; 
   P0_0=~P0_0;  //
   TR1=1;
 }

main()
{  TMOD=0x10;      //模式選擇
   TL1=0xfe;            
   TH1=0xff;
   TR1=1;
   ET1=1;                //允許TR1中斷
   EA=1;
   while(1);
 }