To avoid potentially damaging current caused by floating CMOS input-only pins, it is recommended tying unused controller input pins through a pullup resistor to its associated power supply or through a pulldown to ground unless noted in the Pin Functions. For controller inputs with an internal pullup or pulldown resistor, it is unnecessary to add an external pullup or pulldown unless specifically recommended. Internal pullup and pulldown resistors are weak and must not be expected to drive the external line.

Unused output-only pins can be left open.

When possible, it is recommended to configure unused bidirectional I/O pins to their output state such that the pin can be left open. If this control is not available and the pins become an input, then they must be pulled-up (or pulled-down) using an appropriate resistor unless noted in the Pin Functions.