Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!hplabs!hp-sdd!artecon!sceard!mrm
From: mrm@sceard.UUCP (M.R.Murphy)
Newsgroups: comp.dcom.modems
Subject: Re: null modem cables
Summary: Be wary of frame ground
Keywords: sparks loud noises flashes of bright light
Message-ID: <829@sceard.UUCP>
Date: 9 Sep 88 15:35:47 GMT
References: <8809030943.AA02215@ucbvax.Berkeley.EDU> <2066@stpstn.UUCP>
Reply-To: mrm@sceard.UUCP (0040-M.R.Murphy)
Organization: Sceard Systems, Inc., San Marcos, CA  92069
Lines: 29

In article <2066@stpstn.UUCP> aad@stpstn.UUCP (Anthony A. Datri) writes:
[...simple null modem diagram deleted]
..>
..>A full-blown, general-purpose null-modem cable would be thus:
..>
..>1---------1  (always friendly to include the frame ground)
[...rest of null modem diagram deleted]
..>
..>In short, pins 1,7,8 wired straight, 2x3, 4x5, 6x20.
..>The 4-wire form works for most things (terminals, printers),
..>the full-blown is for things that want hardware handshaking.
..>And, of course, if you've got something like an MTI mux or
..>(shudder) a DMF-32, everything's screwy.
..>
..>
..>-- 
..>@disclaimer(Any concepts or opinions above are entirely mine, not those of my
..>	    employer, my GIGI, or my 11/34)
..>beak is								  beak is not
..>Anthony A. Datri,SysAdmin,StepstoneCorporation,stpstn!aad

Including the 1-1 connection can really be exciting if someone (electrician,
homeowner, facilities group, ...:-) has miswired the AC and reversed
hot and neutral somewhere. The 1-1 connection can then become a fuse.
It's not always a good thing to connect frame-frame.

-- 
Mike Murphy  Sceard Systems, Inc.  544 South Pacific St.  San Marcos, CA  92069
ARPA: sceard!mrm@nosc.MIL   BITNET: MURPHY@UCLACH
UUCP: ucsd!sceard!mrm     INTERNET: mrm%sceard.UUCP@ucsd.ucsd.edu