On 21-5-2010 15:53, clipka wrote:
> Am 21.05.2010 10:18, schrieb Invisible:

>> I have no idea how or why transistors work. But then, the entire _point_
>> of a logic gate is that it doesn't matter _how_ it works. It's a black
>> box. It implements a logical function. That should be all you need to 
>> know.

Wrong. See clipka's comment below. Also it is vitally important to know 
how a logical function is implemented if you are going to use it outside 
the logical specification. In particular the mathematical logical NAND 
is not specified if you leave one input open. What would a Haskell 
implementation do if you leave one input open?

> Note however that this black-box-knowledge should include the interface 
> characteristics - and knowing what goes on in a /simple/ logic gate 
> helps a lot to this end.
> 
> For instance, you should know how many inputs a logic gate output can 
> drive reliably; how an unconnected input behaves; how the gate creates, 
> and how it is affected by, noise on the power rails (and how to deal 
> with that phenomenon); how much current the gate draws, and what 
> parameters affect the power consumption (e.g. a TTL device will draw 
> current primarily due to its internal state, while a CMOS device will 
> draw current primarily due to changes of its internal state); and plenty 
> more such stuff.

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