請教為何中斷不能返回

#include<reg52.h>
#define uint unsigned int 
#define uchar unsigned char
sbit beep=P2^2 ;
sbit key=P3^7;
sbit power=P1^4;
sbit D1=P0^7;
void delay(uint z);
void main()
{
	power=0;
	EA=1;
	EX0=1;
	key=1;
	while(1)
	{
	  while(!key)
	  
	  D1=~D1;
	 
	  while(D1==0)
	  {
	  	beep=0;
		delay(600);
		beep=1;
		delay(600);

	  }
   }
}
void delay(uint z)
{
	uint x,y;
	for(x=z;x>0;x--)
		for(y=100;y>0;y--);
}
void exter0() interrupt 0//中斷服務(wù)程序

{
	D1=1;
	
}