Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each
bit). The Port A output buffers have symmetrical drive characteristics with both high sink
and source capability. When pins PA0 to PA7 are used as inputs and are externally
pulled low, they will source current if the internal pull-up resistors are activated. The Port
A pins are tri-stated when a reset condition becomes active, even if the clock is not
running.
Port A also serves the functions of various special features of the ATmega8515 as listed
on page 67.