What's the input-resistance of any analog/digital pin - so, any chance of blowing the 328p by connecting inputs directly to a voltage source?
The 328p datasheet expresses it as input current leakage (1 ua max) and is equivelent to around 5 meg ohms minimum of input resistance.
Keep in mind that it only applies if the pin is setup (or as default from reset condition) to be an input pin. Once you change the pin to be an output pin, it represents a very low impedenace to either ground or Vcc and a short circuit on a output pin will damage the pin from over current flow. All pins must not be wired to voltages above Vcc +.5vdc or less then ground - .5vdc as that will forward bias the clampling diodes and cause damage.
IIL
Input Leakage
Current I/O Pin
VCC = 5.5V, pin low
(absolute value)
1 ?A
IIH
Input Leakage
Current I/O Pin
VCC = 5.5V, pin high
(absolute value)
1 ?A