I have two Uno's (master and slave), separately powered ...
it's an interesting case when there is no VCC (the vcc input is not powered).
I would disagree somewhat about VCC. VCC input is floating, not grounded at 0V
This is really rocking my world right now. I wonder what horrors I've done leaving a USB CD-ROM plugged in via USB, while being disconnected from power, for instance. I never thought to care.The one thing I've learned while designing electronics is how little I know about electronics. Usually, this occurs when I'm starting to feel proud of myself for something. It sure explains why, when I see an experienced designer's schematic, I think, "that looks awfully complicated for what it does."
What's the accepted form of input protection one should build into their circuits,
I wonder what horrors I've done leaving a USB CD-ROM plugged in via USB, while being disconnected from power, for instance.
I expect it would be quite common for signal sources to be alive and present while the sensing IC is otherwise unpowered.