docs/85355: [patch] Error in the pin numbers of the described connector in the Handbook (serial).

[Gary W. Swearingen]

The following reply was made to PR docs/85355; it has been noted by GNATS.

From: garys at opusnet.com (Gary W. Swearingen)
To: Yar Tikhiy <yar at comp.chem.msu.su>
Cc: jpeg at thilelli.net, docs at freebsd.org
Subject: Re: docs/85355: [patch] Error in the pin numbers of the described
 connector in the Handbook (serial).
Date: Mon, 29 Aug 2005 07:52:16 -0700

 Yar Tikhiy <yar at comp.chem.msu.su> writes:
 
 > It might be reasonable to tell that in general, a null-modem cable
 > is for connecting a DTE directly to another DTE.  AFAIK, null-modem
 > cables can be constructed for synchronous comms, too.  Then, the
 > topic can be narrowed down to async comms.
 
 I doubt if Julien wants to do more rewrites on the section.  But I
 can't resist replying anyway; maybe Yar wants to rewrite it later.
 
 It probably should have some of the cable stuff from the "Serial
 Ports" section which says that a null-modem is AKA DTE-to-DTE cable
 and what DTE is, eg, a computer.  And terminals traditionally have
 included teletypes and printers. (Once there were no CRTs or LCDs.)
 
 > To me, www.hardwarebook.net doen't seem the definite resource.
 > IMHO, if the topic is rather wide, the reader should better be
 > hinted to do a (re)search on the Net instead of pointed to a single
 > resource, which is likely to become incomplete, outdated, or down.
 
 I was thinking the same things.
 
 > Apropos, has there ever been a DTE printer?  I think that printers
 > or sync comms shouldn't belong there if it were told above that we
 > would deal with async DTE-DTE comms only in this section.
 
 Serial printers were once common (I have one) and I think few, if any,
 were configured as DCE (eg, modems); the bulk were DTEs. But sync
 comms don't need to be mentioned; I don't know if FreeBSD can even
 handle it.  I just wanted some note about the large number of
 null-modem designs for different purposes, for folks raised on USB.
 
 > We may show two or three different designs in the handbook if we
 > can tell the reader about their merits.  The problem with the design
 > currently in the handbook is that it is erroneous *and* bogus.  I'd
 > suggest adding another row to the table so that it becomes evident
 > that DTR on this side is connected to DSR+DCD on the other side
 > while DTR on the other side is connected to DSR+DCD on this side.
 
 The Note below the pin-out is supposed to make it evident, and with
 the Note the design is symmetric.
 
 > An RS-232 null-modem cable should be symmetric, to my mind.
 
 A "typical async null-modem cable", yes.  But few of the many RS-232
 null-modem cable designs shown in the book are symmetric, owing to the
 variety of designs of much DTE. (Less true today than yesteryear.)