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

[patchell]

ChristianH wrote:

> Hi all,
>
> I knew this would happen, one century or another.
>
> For years I've been wondering why they kept all those 74 series alive.
> And it's not that I didn't like the situation - I grew up with 74LS, my
> granddad used to use them (um, not quite), never bothered to look at
> that "new" stuff like HCT.
> And in every classic analog poly synth there's LS, so it _must_ be the
> right way to do it... ;-)
>
> I didn't find much on direct replacement on the TI site.
> Now, has anybody here more experience then me? Can LS in existing
> circuits be replaced by 74HCT or 74AHCT (partially, e.g. replacing a
> dead chip)? At a quick glimpse, the data sheet specs look pretty
> compatible to me, if not better. How does it look in practice?

    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).



>
>
> Any comments on how robust the (A)HCTs are? In my experience, the LS
> proved to be rather indestructible (well, sort of, at least they don't
> die immediately e.g. on shorts between pins).

    CMOS is not a rugged as LS.  But I think you will find it comparable to
LS.  It is definately more static sensitive.

>
>
> regards
> Christian
>
> P.S.: Is this _the_ Scott Evans who once maintained the Akai List?
>
> On Fri, 11 Jan 2002 14:21:06 -0800 Scott Evans, Gen Mgr wrote:
>
> > FWIW (if anyone still uses this stuff or has legacy parts to replace):
> >
> > >From the Texas Instrument web site:
> >
> > "ON Semiconductor has recently announced their withdrawal from the LS
> > market. They are taking lifetime-buy orders through May of 2002 with a
> > final delivery date of November 2002. "
> >
> > Texas Instruments offers a cross reference replacement guide for ON
> > Semiconductor parts at their web site:
> >
> > http://focus.ti.com/pdfs/logic/ti_on_ls_xref.pdf
> >
> > Links into the TI-LS page may be found at:
> >
> > http://focus.ti.com/docs/logic/logichomepage.jhtml
> >
> > Scott

--
 -Jim
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