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From: ken@rochester.arpa (Ken Yap)
Newsgroups: sci.electronics
Subject: Re: TTL Questions
Message-ID: <764@sol.ARPA>
Date: Fri, 24-Jul-87 16:41:33 EDT
Article-I.D.: sol.764
Posted: Fri Jul 24 16:41:33 1987
Date-Received: Sat, 25-Jul-87 15:16:35 EDT
References: <1395@crash.CTS.COM> <1008@speech1.cs.cmu.edu> <294@uvicctr.UUCP>
Reply-To: ken@rochester.UUCP (Ken Yap)
Distribution: na
Organization: U of Rochester, CS Dept, Rochester, NY
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|I read a neato book once by a guy who actually went out and tested things
|like this, measured the impedance of wirewrap, found out how many bypass
|capacitors you actually need, etc.  He said that open TTL inputs WILL NOT
|GLITCH even under the most extreme conditions.  Remember, before you flame,
|he actually made circuits and tried it out...  He also pointed out that
|you can short one output per package indefinitely for testing purposes
|with no harm to the chip - actually pretty handy to know.

That is comforting to know, but I see no reason to tempt fate
unnecessarily.  One easy way of dealing with spare inputs on N/AND,
N/OR gates is to tie them in parallel to another input.  As opposed to
pulling them high with a resistor to +5V.  Provided you stay within the
load capacity of the driving gate.

CMOS inputs should not be allowed to float, of course.

	Ken