[sdiy] [OT] LS Series (Low Power Schottky Logic)

[Ingo Debus]

patchell wrote:
>     In general, 74HCTxxx and 74AHCTxxx can replace LS, however, I have seen
> a lot of stuff that used LS that did not have much in the way of power
> supply bypassing.  LS, while it should be bypassed, evidently does pretty
> good without it.  HCT type stuff (CMOS) may or may not be forgiving in these
> situations.  But all things being equal, a well designed logic circuit in LS
> can be implemented easily in HCT (notice I said well designed).

Yes, I remember my first design that failed *because* of too few
decoupling caps was indeed one of my first HCT designs :-)

Another thing to watch out for is open inputs. It's bad design practice,
but an open LS input is usually high level. An open HCT input can be
anything - the circuit can even work for several minutes, then stop.
Just like standard CMOS logic.

HC(T) aren't as good as LS when used as bus/line drivers. But there are
other CMOS type (BCT) that can be used here.

"Quasi-analog" circuits, like quartz oscillators, eventually differ in
the LS and the HCT version.

Ingo