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RE: ECM Bench kelp needed



Although the input thresholds are different, since Bruce's circuit is only
driving 1 or 2 inputs from any given output, the output of an HC part will
EASILY swing between 0 and 5V.  One needs to look at the Voh vs. current on
the HC part and compare Voh to the Vih (min) spec on a 2732 or LS or other
digital part.  There won't be a problem.  If LS parts are available, use
them.  If HC parts are the only available easily, they will be fine.  Always
remember, for low current drive virtually every digital output in the world
will swing to within 1% of the supply rails.
Steve

-----Original Message-----
From: thergen@svn.net [mailto:thergen@svn.net]
Sent: Thursday, January 13, 2000 10:49 AM
To: gmecm@efi332.eng.ohio-state.edu
Subject: Re: ECM Bench kelp needed


Bruce,

Try:
http://www.digikey.com/scripts/US/DKSUS.dll?Detail?Ref=100075&Row=46625
which is a 74ls161 (digikey part search on 74ls161).

The 74S161 is in the Schottky TTL family - faster, uses more power, inputs
require more current.  It would probably work.

The 74HC161 is in the High Speed CMOS family - wider power supply range,
low power, *different input threshold than regular TTL*.  The inputs may
not be driven reliably by TTL or certain eproms like a 2732 (check the Voh
spec on the eprom output and the Vih spec on the 74HC161 input).

Don't use the HC part.

The HCT family is more compatible than HC with the various flavors of TTL.

Hope that helps,
Tom


On Thu, 13 Jan 2000, Bruce Plecan wrote:

> I have a wiring diagram for my DIS signal generator that uses two
74LS161s.
> I have been every where locally and no one has them.   I have found some
> similiar part nos. at Digi-Key,  those being a:
> DM74S161-ND,   and a
> MM74HC161N-MM
> Can I use these?, one perferable to the other?, what's the difference in
the
> three.
> Thanks
> Grumpy
>