sbliven:
I'm working on a project that requires pins to be in a high-impedance state. For most pins this works fine by setting the pin to input and disabling the pull-up resistor. However, when I do this with pins 0 and 1 they will source enough current to dimly light an LED. Presumably this has something to do with their dual function for USB. Anything I can do to disable this behavior, either in hardware or software?
Pins 0 and 1 are the serial interface. When the USART is enabled it overrides the normal pin operation.
You can disable it by clearing the relevant bits in UCSRnA (see datasheet).