title: yikes invalid device signature
body: <p>i am using arduino isp to program a ATtiny2313 avr microcontroller. 
  Here is the probelm, 
  when i was programming the avr chip using the default fuse values, everything worked just fine. 
  But then, i changed the fuse bytes as i wanted to use an external 16 MHz crystal. 
  When i changed the lfuse value from 0x64 to 0xff (as per the calculation of the fuse bits), the microcontroller stopped responding. </p>
  
  <p>Now everytime i try to program the microcontroller using arduino uno isp, i get an error message : 
  avrdude: Yikes!  Invalid device signature.
  avrdude: Expected signature for ATtiny2313 is 1E 91 0A</p>
  
  <p>and then the fuse bytes shown after verification, very strangely are all set to 0x00 : 
  avrdude: safemode: Fuses OK (H:00, E:00, L:00)</p>
  
  <p>i dont understand what the hell is happening and i have spent hours trying to figure out the probelm. </p>
  
  <p>should the 16Mhz crystal be connected to the microcontroller while programming ?</p>
  
  <p>PLEASE HELP !</p>