case 2: 
   Reader_B = LOW;  // pull 1_Wire line low 
   us_Delay(29);    // leave it low for 480us 

   Reader_B = HIGH; // allow line to return high 
   us_Delay(3);    // wait for presence 

   if(Reader_B)    // if line is high 
      return 0;    // no part presence 
   else 
   { // get presence signal 
      while(!Reader_B); // wait for end of timeslot 
      return 1; // 1=presence, 0 = no part 
   } 
   break;