Unconnected pinsIf some pins are unused, it is recommended to ensure that these pins have a defined level. Eventhough most of the digital inputs are disabled in the deep sleep modes as described above, floatinginputs should be avoided to reduce current consumption in all other modes where the digitalinputs are enabled (Reset, Active mode and Idle mode).The simplest method to ensure a defined level of an unused pin, is to enable the internal pullup.In this case, the pullup will be disabled during reset. If low power consumption during reset isimportant, it is recommended to use an external pullup or pulldown. Connecting unused pinsdirectly to VCC or GND is not recommended, since this may cause excessive currents if the pin isaccidentally configured as an output.
If a pin is wired to be an output, wouldn't enabling the pullup be almost the same as turning the pin high?
I think we're talking past each other.
Wen using digital outputs to drive external circuitry (e.g. a transistor power switch, on/off motor controller, etc.) we typically need to add an external pull-down resistor to make sure whatever is connected remains idle/safe during power on, reset or whenever our software is not in control.