[Alan Anderson]

There is no "neutral" on a digital I/O pin. As an output, it will be either ground (logic 0) or +5 (logic 1). Each pin has a resistor to +5, so even if nothing is conneted, it will be pulled high (logic 1) if it's set to be an input.

We of course set the output to 1 as part of the program initialization. I don't remember whether we do it before or after it is configured as an output. The PROG signal must be grounded for a certain time before it actually takes effect, so a very brief moment when the digital output is low doesn't hurt.