Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!rutgers!mit-eddie!uw-beaver!fluke!ssc-vax!uvicctr!collinge From: collinge@uvicctr.UUCP (Doug Collinge) Newsgroups: sci.electronics Subject: Re: TTL Questions Message-ID: <294@uvicctr.UUCP> Date: Thu, 23-Jul-87 11:48:36 EDT Article-I.D.: uvicctr.294 Posted: Thu Jul 23 11:48:36 1987 Date-Received: Sat, 25-Jul-87 14:54:48 EDT References: <1395@crash.CTS.COM> <1008@speech1.cs.cmu.edu> Reply-To: collinge@uvicctr.UUCP (Doug Collinge) Distribution: na Organization: University of Victoria, Victoria B.C. Canada Lines: 26 In article <1008@speech1.cs.cmu.edu> phd@speech1.cs.cmu.edu (Paul Dietz) writes: >In article <1395@crash.CTS.COM> rpluth@pnet01.CTS.COM (Ron Pluth) writes: >> 2. I've worked with Schottky and Low-power Schottky logic >>chips in the lab, and have seen that a no connection to inputs, >>such as a simple AND or OR gate, even sometimes in MUX's and >>others, drives the input high. Is this guaranteed true? >Never, never, never, never, never assume this! This is the quickest way >to get into trouble! Yes, standard TTL floats high by nature, but any >mild strays are enough to glitch it to another state! 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. -- Doug Collinge School of Music, University of Victoria, PO Box 1700, Victoria, B.C., Canada, V8W 2Y2 collinge@uvunix.BITNET decvax!uw-beaver!uvicctr!collinge ubc-vision!uvicctr!collinge