About Inputs and Outputs

Most general purpose pins on a microcontroller can function in one of two modes: input mode, or output mode.

When acting as an input, the pin will be placed in high impedance state. The microcontroller will then sense the pin, and the program can read the state of the pin and make decisions based on it.

When in output mode, the microcontroller will connect the pin to either Vcc (the positive supply), or Vss (ground, or the negative supply). The program can then set the state of the pin.

Great Cow BASIC will attempt to determine the direction of each pin, and set it appropriately. However, if the pin is read from and written to, then then pin must be configured to input / output mode by the program, using the appropriate Dir commands.