I have a 1284P that acts as a master that is talking to an ESP8266 and an Arduino Nano over the two hardware serial lines. I’ve noticed that when I disconnect power to the nano it will still run just fine, drawing power through the serial lines I guess.
I want to put both of these devices where I can control power to them from the 1284 with a mosfet. So my question is how can I do that and avoid any parasitic power to those boards? Will it help to hold the Serial pins in a given state? I don’t really understand what the fundamental problem is. Should I put the power control to cut the power or the ground? Do I need to “park” the serial lines somehow?