>>> IIRC I think the specs said that TTL inputs would be at a logical 1 
>>> if there was no connection. (Internal resistor to Vcc) 
>>
>> Oh.
>>
>> Well that would be a problem then. I was assuming it would be logic 0. 
>> o_O
> 
> Starting middle of September I'll be teaching digital technology in the 
> first year of the University of Applied Science in Amsterdam. If you 
> happen to be around, just drop in. I think I will do the 7400 in the 
> week of Sept 21. ;)

Heh. I doubt it - but nice idea. ;-)

> As others have said, the original TTL series by Texas Instruments acted 
> as if a one was present if left open. All other gates should do the same 
> because of backwards compatibility. That includes the CMOS pin 
> compatible replacements. I have actually seen rare default 0 gates but I 
> would consider those faulty.
> 
> When designing the rule is not to leave inputs open. Not even for gates 
> you don't use. One reason is that they could pick up interference which 
> could result in unpredictable behaviour. For CMOS gates it could also 
> result in useless power consumption. In any case the inputs are often 
> next to one another like in the 7400. It is just as easy to wire them 
> together (connecting them to ground (for NOR gates) or the positive rail 
> (for NAND gates) is often more complicated).

Mmm. This I was not aware of...

> Oh, and if you want to build your own computer, I'd suggest using also 
> other components apart from the 7400.

OOC, exactly how much space do you recon it would take to build 64KB out 
of discrete NAND gates?

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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