Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!cornell!rochester!uhura.cc.rochester.edu!!syap
From: syap@cc.rochester.edu (James Fitzwilliam)
Newsgroups: comp.dcom.modems
Subject: Re: null modem cables
Summary: Special adaptor for machines that aren't handshaking properly
Message-ID: <9@ur-cc.UUCP>
Date: 8 Sep 88 05:04:13 GMT
References: <8809030943.AA02215@ucbvax.Berkeley.EDU> <2066@stpstn.UUCP>
Sender: news@uhura.cc.rochester.edu
Reply-To: syap@cc.rochester.edu (James Fitzwilliam)
Organization: Gadgetland USA
Lines: 36

In article <2066@stpstn.UUCP> aad@stpstn.UUCP (Anthony A. Datri) writes:

[... two good diagrams omitted...]

*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. -- see below
*And, of course, if you've got something like an MTI mux or
*(shudder) a DMF-32, everything's screwy.

I had a different unusual problem when making a null adaptor to connect my
laptop and my Macintosh's modem cable (a commercial Din-8 to RS-232).  The
laptop wanted a handshake and wasn't getting it from the cable, so I wired
the adaptor thus:

2 --------- 3
3 --------- 2
7 --------- 7

4 --     -- 4
    |   |
5 --     -- 5

Each computer handshakes itself, and is constantly in a ready-to-transmit
state.  Loss of the handshake's function (to make sure both ends are ready
for data transfer) is irrelevant, since you have both machines under your
control and can see for yourself whether they're both turned on.  Probably
you won't encounter this situation, but just in case... I was scratching my
noggin for quite awhile on it!

                                              James

domain: syap@vera.cc.rochester.edu
  path: rochester!vera!syap  (I think...)          "Piano is my forte"  (-:
 GEnie: FITZWILLIAM

===========================================================================