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Path: utzoo!linus!decvax!decwrl!amdcad!fortune!foros1!redwood!rpw3
From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.micro
Subject: Re: mysterious resistor
Message-ID: <75@redwood.UUCP>
Date: Sat, 3-Nov-84 05:48:53 EST
Article-I.D.: redwood.75
Posted: Sat Nov  3 05:48:53 1984
Date-Received: Sun, 4-Nov-84 04:57:19 EST
References: <4559@utzoo.UUCP>
Organization: [Consultant], Foster City, CA
Lines: 23

+---------------
| ...The mystery part is, there is a 22 megohm resistor across
| the "inside" ends of the 100k resistors.  Any idea what it's for?
+---------------

Just a guess... in case the ring detector gets connected to a long telephone
line that is NOT connected at the other end (the C.O.), the 22 meg resistor
will prevent static charge buildup which could eventually puncture the
.01 capacitor (which has only a finite breakdown voltage). It may also be
(and this is more likely) to protect the whole thing during packing and
shipping (in plastic wrappings).

I have done similar things designing interface cards (controllers) which
had MOS pins straight on the bus (and no TTL) -- put a very high resistor
between the pin and +5 (which is == 0 during shipping) to prevent static
buildup during shipping and handling.

Rob Warnock

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