Not sure which forum this should go to, so trying here.
The M328P has digital disconnects on ADC inputs since logic inputs can cause a lot of power (in relative terms, I guess) to be drawn from Vcc when inputs are held around Vcc/2.
I cannot tell if something similar is used in the Mega0/1 devices or if there is an automatic disconnect built in.
Can someone point to any details on this beyond the lack of details? Or, am I just missing the reference in the documentation?