Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site islenet.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!seismo!lll-crg!dual!islenet!bob From: bob@islenet.UUCP (Bob Cunningham) Newsgroups: net.dcom Subject: Re: lightning, PACXs and computers (followup) Message-ID: <1507@islenet.UUCP> Date: Sat, 17-Aug-85 06:32:59 EDT Article-I.D.: islenet.1507 Posted: Sat Aug 17 06:32:59 1985 Date-Received: Tue, 20-Aug-85 21:25:49 EDT References: <1397@islenet.UUCP> <29116@lanl.ARPA> <1028@ulysses.UUCP> <1831@ecsvax.UUCP> <1465@islenet.UUCP> <1242@umcp-cs.UUCP> Organization: Hawaii Institute of Geophysics Lines: 22 > >... All Computer equipment and auxiliary racks within a room should > >be securely grounded to a single point with generous-size braided > >ground straps. It seems to be a good idea to tie down all incoming > >terminal grounds (RS232 pin 7) to that same point. . . . > > Everything I thought I knew about grounding says you never tie signal > ground (pin 7) to frame ground. Am I wrong, or is this a Big Mistake? This is an almost-counter-intuitive trick I picked up at another site where we were having a few seemingly-weird problems with RS232 signals that seemed to "float" far too much. The point is to make sure that -- at the computer port side -- all the signal grounds sit at the same potential. Easiest way to accomplish this is to tie them all to the reference ground. We don't carry pin 1 (frame ground) from the terminals to the computer. From my experience, it works, even though there is potential (no pun intended) ground loop problem with remote terminals that also tie pin 7 to their frame ground, and have a different reference ground (say, in another building). -- Bob Cunningham {dual|vortex|ihnp4}!islenet!bob Hawaii Institute of Geophysics Computing Facilities Honolulu, Hawaii