#include<reg51.h>
#include <stdio.h>
sbit P2_0=P2^0; //trigger pin
sbit P1_0=P1^0; //echo pin

delay()
{
  int i;
  for(i=1;i<=30;i++)
  ;
}
delayms()
{
  int i;
  for(i=1;i<=9;i++)
  ;
}
//----------------------------------
init_rs232()	   /* <9600 N 8 1>  */
{
  SCON=0x50;
  TMOD=0x21;
  TH1 =253;
  TR1=1;
  TI =1;
 }
//-----------------------------------
void SCON_int(void) interrupt 4	
{	
	
  if(TI==1)
      TI=0;
  else
    {
      RI=0;
    } 	
}
//----------------------------------
test()
{
  int d;
  
  while(1)
  {
  
  while(P1_0==0);
  TR0=1;
  while(P1_0==1);
  TR0=0;
  d=TH0*256+TL0;
  printf(" %d ", d);
    TH0=TL0=0;
  P2_0=1;
  delay();
  P2_0=0;
  delayms();
  
  }
}
//-----------------------------------
main()
{   
  P1=0xff;   
  P2_0=1;
  delay();
  P2_0=0;  
  delayms();
  init_rs232();
  test();

}