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From: cdh@BBNCD3.ARPA (Carl D. Howe)
Newsgroups: net.micro
Subject: Re:  APPLE ][ to KAYPRO on a null modem
Message-ID: <9986@brl-tgr.ARPA>
Date: Tue, 16-Apr-85 09:12:27 EST
Article-I.D.: brl-tgr.9986
Posted: Tue Apr 16 09:12:27 1985
Date-Received: Thu, 18-Apr-85 07:48:46 EST
Sender: news@brl-tgr.ARPA
Lines: 12

There is often much confusion on the role of pin 1 in RS-232.  As it turns out,
both Dick Binder and Rob Warnock are right.  It is the responsibility of the
DTE (read terminal or computer) in a system to connect pin 1 of an RS-232 cable
to frame ground to prevent radiation from the cable, provide shielding, etc.
However, the DCE (read modem) DOES NOT connect pin 1 to frame ground to avoid
ground loops between the DTE and the DCE.  A null modem simulates two DCE's
back to back.  So when you are making a null modem,
it is best to leave pin 1 open on both sides; the DTE's have already tied pin 1
to their frame grounds so the cable's won't radiate, and your leaving them
separate from each other prevents ground loops.

Carl