Re: OT - TTL Circuit: Pullup vs Supply

At 3:12 AM -0500 9/8/06, Matt J. McCullar wrote:
> > I could swear I recall reading something in the "applications notes"
>> section of one of my old TTL books about a pull-up (or pull-down) resistor
>> providing improved noise immunity, which might be important for control
>> pins (such as reset* / preset* pins on flip-flops or shift registers)
>whose
>> function isn't needed in the application in question...
>>
>> ...but I'll be damned if I can *find* the book in question! The books
>> I have handy don't say anything about this... so I've either
>lost/misplaced
>> the book that did, or I'm completely misremembering having ever read it in
>> the first place. :)
>> --------------------------------------------------------------------------
>---
>
>I'll try to look in Don Lancaster's _TTL Handbook_ (or whatever he calls it)
>for this info. My copy is at work, not at home.
>

Page 12/13 of Don Lancaster's bible "TTL COOKBOOK" states that inputs
should be either tied directly to Vcc or to a "logically similar
input". he goes on to state that the military practice of tying
unused inputs to Vcc via a 1K resistor is "usually not justified by
the benefits and causes more problems than it solves".

I recommend that any tech without a copy of this and CMOS COOKBOOK
should get them into their library ASAP! eBay often sells these for
under $20US, and Amazon.com and other booksellers are often much less
for used books.

John :-#)#
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Received on Fri Sep 8 12:09:04 2006