Build your own Apollo Guidance Computer

[Guy Sotomayor]

der Mouse wrote:
>> Is there a guide somewhere to the different families of logic, such
>> as RTL, TTL, LSTTL (never heard of that one)
>>     
>
> LSTTL = Low-power Schottky TTL: basically, TTL done with low-power
> Schottky technology.  (http://en.wikipedia.org/wiki/Schottky_barrier
> has more than you probably want to know about what Schottky means as
> applied to semiconductor logic.)
>   
LS usually has the speed of TTL with the power dissipation of L.

Other variations:

74Hxx
74Lxx
74Sxx
74ASxx
74ALSxx
74Cxx
>   
>> Also, some are Schmidt Triggered?
>>     
>
> (Schmitt, I think.)  I suspect most logic families have something
> functionally equivalent to Schmitt triggers (inputs with hysteresis).
>
> As for a guide to the families, I can't help much there.  I know that
> there exists CMOS which is signal-level-compatible with TTL (I think
> they're the 74HCT parts), but that's about where my knowledge ends.
>
> You might also add ECL to your list.  It stands for Emitter-Coupled
> Logic, and I have gained the impression that it's fast and
> power-hungry, but further deponent sayeth not.
>   
ECL is fast because it doesn't put the transistors into saturation or 
cutoff (ie it's operating in the "linear region").  This means that no 
time is required to move "large" amounts of charge (electrons) into or 
out of the base of the transistor which is necessary to "saturate" the 
transistor.  This is why it is so power hungry...it's operating in the 
"linear" region so current is always flowing through it and it's acting 
as a resistor (ie causing a voltage drop across the part).

-- 

TTFN - Guy