So lately I’ve been moving away from the Arduino’s IDE software and getting into coding the AVRs directly. At first I just used a spare 328p I bought some time ago on breadboard and wired up a power supply. However I started thinking that since I had an Uno and Duemilanove that I should just use one of those since I could also make use of the protosheild to make things a bit easier. Connecting an AVR programmer and just writing to the 328p wasn’t an issue. The problem came about with timing. The Arduino is running off a 16MHz external clock and I wanted to switch it back to the 1MHz factory default.

Fixing this problem just took a quick glance at the datasheet. The default low and high fuse byte values are 0x62 and 0xD9 and for the the Arduino’s 328p they come set at 0xFF and 0xDA. Then I just just connected my USBtiny to the Arduino normal and ran avrdude to write the fuse values.

avrdude -p m328p -c usbtiny -U lfuse:w:0x62:m -U hfuse:w:0xd9:m

And now it’s running off the internal 8MHz clock with the CKDIV8 fuse set which brings it to the factory default of 1MHz.