>> 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.

Hmm... Oh dear.

>> 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.

Really? I thought it was 4.5V - 5.5V 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.

http://en.wikipedia.org/wiki/Hi-Z
http://en.wikipedia.org/wiki/Three-state_logic

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