Date: Mon, 29 Aug 2005 07:52:16 -0700 From: garys@opusnet.com (Gary W. Swearingen) To: Yar Tikhiy <yar@comp.chem.msu.su> Cc: docs@FreeBSD.org Subject: Re: docs/85355: [patch] Error in the pin numbers of the described connector in the Handbook (serial). Message-ID: <3gbr3gvlr3.r3g@mail.opusnet.com> In-Reply-To: <20050829083036.GA79816@comp.chem.msu.su> (Yar Tikhiy's message of "Mon, 29 Aug 2005 12:30:36 %2B0400") References: <200508272040.j7RKeKaQ018390@freefall.freebsd.org> <20050829083036.GA79816@comp.chem.msu.su>
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Yar Tikhiy <yar@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 resource, which is likely to become incomplete, outdated, or down.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.)
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