Every AVR microcontroller, from the ATtiny in your thermostat to the ATMega in your Arduino, stores its configuration in a series of fuse bits. These fuse bits control settings such as the ...
A Direct AVR Parallel Access ... If you try to run the chip’s clock at full speed (by changing fuse settings… more in Part 3) you won’t be able to use a DAPA cable to talk to it any longer.