Full datasheet covering the ATmega325, ATmega3250, ATmega645 and ATmega6450 AVR microcontrollers, a 2.69 MB PDF. The four-digit 3250 and 6450 parts are the higher pin-count package versions of the same cores, so pinout tables differ between them. A technician consults it to map ports, power and programming pins on the actual package fitted, check absolute maximum ratings, and configure fuses before writing firmware. Confirm the package and pin count on the board before following any pin diagram.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @datasheet. Enginerys does not host this file.
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