Changing AVR fuse values in an unintended way can render the microcontroller practically dead. For example you might have altered clock source bits in a way that the processor cannot be programmed anymore. Trying to fix the problem by applying default fuse values fails:
$ avrdude -p attiny85 -c usbasp -U lfuse:w:0x62:m -U hfuse:w:0xdf:m -U efuse:w:0xff:m
avrdude: warning: cannot set sck period. please check for usbasp firmware update.
avrdude: error: program enable: target doesn't answer. 1
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.
avrdude done. Thank you.
Even using slower bitclock does not necessarily work anymore:
$ avrdude -p attiny85 -c usbasp -U lfuse:w:0x62:m -U hfuse:w:0xdf:m -U efuse:w:0xff:m -B1000 -F
avrdude: set SCK frequency to 1000 Hz
avrdude: warning: cannot set sck period. please check for usbasp firmware update.
avrdude: error: program enable: target doesn't answer. 1
avrdude: initialization failed, rc=-1
avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x88fb38
avrdude: Expected signature for ATtiny85 is 1E 93 0B
avrdude done. Thank you.
Atmel ATtiny datasheet chapter "High-voltage Serial Programming" describes alternative way of programming ATtiny microcontroller. With this mechanism it is possible to bring the MCU back to life.
The code in this project uses Arduino Nano to re-program ATtiny85 microcontroller fuses to default values using the HVSP method. Normal serial programming method can be used again after running the program.
Following schema describes the circuit for running the programmer. The circuit requires 12V voltage source for applying 12V to RESET pin of ATtiny85.
