I would be pulling my hair out over this, if it was long enough...
I am looking on DigiKey for a Sanguino compatible ATMega 644... I know that I need the 644P... There are 3, and all of the specs are EXACTALLY the same!
They are:
ATMEGA644PA-PU
ATMEGA644P-20PQ
ATMEGA644P-20PU
I would guess the ATMEGA644P-20PU, but I'm not sure, so I thought I'd ask...