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From: colin@vu-vlsi.UUCP (Colin Kelley)
Newsgroups: net.dcom
Subject: RS-232 pin 1, line noise
Message-ID: <405@vu-vlsi.UUCP>
Date: Mon, 3-Nov-86 22:39:03 EST
Article-I.D.: vu-vlsi.405
Posted: Mon Nov  3 22:39:03 1986
Date-Received: Tue, 4-Nov-86 08:27:48 EST
Organization: Villanova Univ. EE Dept.
Lines: 25

I recently set up an Epson printer with a serial interface to an ABCD switch
(i.e. a 1-of-4 switch) in order to share the printer between 4 PClones.  The
Epson serial interface manual was very good, and I had no trouble getting
it to work with hardware handshaking, using only SG, RD, and DTR on the
printer end.  However, I didn't (and still don't!) know what to do with pin 1
(Frame Ground, or Protective Ground).

I'm now finding that the longest cable (~50 feet) is having trouble with
garbage occasionally introduced by noise.  I tried dropping the baud rate
from 9600 to 2400 (still faster than the printer) but that didn't help.
How can I remedy this?  Should FGs of each device been tied together?  Could
not doing this have lead to line noise?

Also, the cable is shielded, but I didn't do anything with the shielding.
Should it be grounded to the connectors, or one of the pins?  On one or both
of the machines?

I do have maybe 10 feet of slack which I could cut of if shortening the cable
20% might help...(The other three cables are closer to 40 feet, and they all
work fine.  However, the cable in question goes through 2 walls, and may be
passing some noise source that I'm not aware of.)

Thanks for any help!

			-Colin Kelley ..{cbmvax,pyrnj,psuvax1}!vu-vsli!colin