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From: wetter@tybalt.caltech.edu (Pierce T. Wetter)
Newsgroups: comp.sys.mac
Subject: Re: EXACT screen refresh rate, and other items
Message-ID: <2914@cit-vax.Caltech.Edu>
Date: Wed, 3-Jun-87 05:26:50 EDT
Article-I.D.: cit-vax.2914
Posted: Wed Jun  3 05:26:50 1987
Date-Received: Sat, 6-Jun-87 10:33:59 EDT
References: <71@wjh12.HARVARD.EDU> <1719@umd5.umd.edu> <2141@husc6.UUCP> <2895@cit-vax.Caltech.Edu> <4619@utah-cs.UUCP>
Sender: news@cit-vax.Caltech.Edu
Reply-To: wetter@tybalt.caltech.edu.UUCP (Pierce T. Wetter)
Organization: Calfornia Institute of Technology
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In article <4619@utah-cs.UUCP> cetron@utah-cs.UUCP (Edward J Cetron) writes:
>
>	wrongo, a good switch debouncer can be made with a single quad nand
>gate as I recall (ttl 7400??) and two jumpers...no clock not nothing, you
>could also use a 555 timer in monostable mode, or even a one-shot......and
>these chips in quantity aren't more than a penny or a dime..

     The Mc14490 is specifically a Hex switch debouncer which works as I 
described. _Yes_ it is possible to debounce a switch any of a millon different
ways. One Shots, RC networks and inverters, latches etc. All of those require
other components such as resistors and capacitors or must be initialized 
(latches). These all make the board a little more complicated. If you realize
that doing the debounce in software using the 60Hz interrupt costs you maybe
absolutely nothing since for most purposes knowing the button state more 
accuatly then 1/60th of a second is rediculous. (The Mac doesn't actually 
debounce the mouse it only reads it once every 60th. If the mouse has changed
state it posts an event.) If you really need to know the mouse state more 
accuratly then that, read the Via...
Pierce Wetter

Politician, n.:
	From the Greek "poly" ("many") and the French "tete" ("head" or
"face," as in "tete-a-tete": head to head or face to face).  Hence
"polytetien", a person of two or more faces.
		-- Martin Pitt

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wetter@tybalt.caltech.edu

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