> 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".
Bingo! I xeroxed that very page out of the _TTL Cookbook_ (or _To Serve
TTL_) this afternoon and highlighted that very passage.
I also looked in a Fairchild TTL databook and it said one reason for
employing the pullup resistors on inputs was to prevent shorts should the +5
volt power supply accidentally drift too high in value. Some TTL inputs
have emitter-type inputs, and pullups are recommended, but other TTL inputs
are diode-type and so protective resistors are not normally required.
Matt J. McCullar
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Received on Fri Sep 8 22:08:09 2006
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