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>>> 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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