Testing in SLEEP_MODE_PWR_DOWN:All pins as outputs, and LOW: 0.35 µA (same as before).All pins as outputs, and HIGH: 1.86 µA.All pins as inputs, and LOW (in other words, internal pull-ups disabled): 0.35 µA (same as before).All pins as inputs, and HIGH (in other words, internal pull-ups enabled): 1.25 µA.
wSo it seems like a good practice to set all unused pins to low.
Or do nothing, as they default to inputs ?
So the point is to not let the pins be in a floating state?
What doesn't make sense to me...
What doesn't make sense to me is that gammon's tests with pullups on (as atmel suggests) has higher power consumption than when the pins are left floating (which atmel says will result in increased power consumption)....
Anyway in all sleep modes except for Idle sleep the input digital buffer is disabled (unless the pin is used as a wake up source) so there should be no difference if the pin is HIGH, LOW or even floating. From my tests the worst case current consumption of a floating pin is 100uA, but is much less typically (@ room temperature!). I think the additional current consumption even with all pins floating is small compared to the current consumption of the CPU running @16MHz.