Is it safe to use D0 and D1 (RX and TX) on the Uno for GPIO? For example, turning on and off an LED. I know the LED(s) would flicker while programming, but is it safe for the ATMEGA8U2 to be getting weird signals, even on it's TX line?
I see there are 1k resistors between the ATmega 328 and ATmega 8U2. I guess that ensures safety, but does the 8U2 use high impedance unless transmitting (sending on TX)?
I think the pull-ups make it a bit of a problem. For example, when I connect LEDs up to my Uno, pins D0 and D1 are usually lit up.
I would steer away from doing that, there might be better alternatives.
I think you can drive those pins low (if in output mode) but you may have trouble using them as inputs.
I want to use them as outputs only, and drive them LOW vs. HIGH (I don't need a high impedance state).
So, it's safe as far as the ATmega 8U2 is concerned?
I think the 1K resistors will protect the 8U2.