> Uh... OK. I never did that before - but hey, maybe that's why half my 
> circuits didn't work?

Hehe maybe, you certainly shouldn't assume that a not-connected or floating 
input will be treated as logic 0.

> Damnit, I thought digital electronics was just about on or off. :-/

It is if you follow the specifications of the particular logic family you 
are using, IIRC TTL is something like 0-0.8V for logic 0, and 2.5V and above 
for logic 1.

> You speak of "3-valued logic" with it's "Hi-Z" mode?

I don't know what it's called, but I remember it when we were doing simple 
memory circuits at university, you need to be able to output either 0,1 or 
floating to the data bus.

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