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First of all I emphasize that unfortunately none the following attempts of reprogramming fused AVRs was successful in my case. Therefore this is more a personal documentation of what did not work, rather than a tutorial on how to get AVRs reprogrammed.

The general problem is, that once the fuse bits of an AVR are set to except an external clock source, the AVRs can in theory only be reprogrammed when they have that external clock source during the reprogramming process as well. In practice it is much more complicated.

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Here some images and schemes for the correct wiring to programm an ATtiny85 microcontroller:


Here one can see the pin description of the ATtiny85:


And here a wiring scheme. The pin allocation of the 6-pin plug is seen from above the plug, which gets really confusing when you have to put the wires right.Furthermore its quite hard to get it clearly laid out:


Here the pin allocation of the 6-pin plug, when you look into the holes of the plug:

The communication works on the ‘Serial Peripheral Interface Bus‘. In the next picture you can see the pin allocation a little better (top > down like in the picture):

  • ground (GND)
  • master output, slave input (MOSI)
  • power supply (VCC)
  • master input, slave output (MISO)
  • source clock (SCK)
  • reset (RST)


In order to get a fast feedback, if the programming really worked, I took a little LED blink sample code:

* blink.c
* Created on: 22.09.2012
* Author: Dario
/*Filename: blink.c */
#define F_CPU 8000000UL
#include <avr/io.h>
#include <util/delay.h>
int main (void)
  //Set PORTB.3 to be output (physical pin #3 on the ATTINY85)
  DDRB = 0b00001000;
  while (1) {
// //Set PORTB.3 high
    PORTB = 0b00001000;
// //Set PORTB.3 low again
    PORTB = 0b00000000;
  return 1;

Related Github Code Repository

Here you can find most of the code I used. Also check out the Github of my superviser Auérlien. In the course of that, I also installed TortoiseGit for an easier commit/push of code into my Github repository.