Currently I'm a bit confused about that single triangle from that schematics used by an AVR-Microcontroller. Currently I've figured out, that the:
is on the AVR an configuration-Register (What is IN, what is OUT)
is on the AVR a register for writing or setting the Pull-Up-Register.
is on the AVR a register for read-only
So the next step for me is to understand that triangle. I've searched for that and found similar symbols. One was an AND-Gate and the otherone a tri-state-logic (buffer). Has somebody an idea what kind of job the triangle implements?