3.2 Configuration

Most MCUs allow software configure whether a physical pin be used as input or output. On the ATMega128 (and other members of the AVR family), each binary I/O pin has two bits for configuration:

• direction: whether the pin is input or output
• state: for an output pin, whether it should drive high or low

In addition, there is also a ``sense'' or ``input'' bit for each binary I/O pin that reports either a 1 (for a high voltage) or a 0 (for a low voltage) at the pin.