From owner-freebsd-alpha Wed Jan 16 13:50:13 2002 Delivered-To: freebsd-alpha@freebsd.org Received: from srv1.cosmo-project.de (srv1.cosmo-project.de [213.83.6.106]) by hub.freebsd.org (Postfix) with ESMTP id 5D67037B402 for ; Wed, 16 Jan 2002 13:50:07 -0800 (PST) Received: (from uucp@localhost) by srv1.cosmo-project.de (8.11.6/8.11.6) with UUCP id g0GLnx637291; Wed, 16 Jan 2002 22:49:59 +0100 (CET) (envelope-from ticso@cicely8.cicely.de) Received: from mail.cicely.de (cicely20.cicely.de [10.1.1.22]) by cicely5.cicely.de (8.12.1/8.12.1) with ESMTP id g0GLoIZ9082028; Wed, 16 Jan 2002 22:50:19 +0100 (CET)?g (envelope-from ticso@cicely8.cicely.de) Received: from cicely8.cicely.de (cicely8.cicely.de [10.1.2.10]) by mail.cicely.de (8.11.0/8.11.0) with ESMTP id g0GLoIW06550; Wed, 16 Jan 2002 22:50:18 +0100 (CET) Received: (from ticso@localhost) by cicely8.cicely.de (8.11.6/8.11.6) id g0GLoGn53313; Wed, 16 Jan 2002 22:50:16 +0100 (CET) (envelope-from ticso) Date: Wed, 16 Jan 2002 22:50:16 +0100 From: Bernd Walter To: Terry Lambert Cc: Trevor Johnson , Riccardo.Veraldi@fi.infn.it, freebsd-alpha@FreeBSD.ORG Subject: Re: DEC3000/300 Message-ID: <20020116225016.N50371@cicely8.cicely.de> References: <20020116023458.E17814-100000@blues.jpj.net> <3C45DF84.5990A4E4@mindspring.com> <20020116214931.M50371@cicely8.cicely.de> <3C45EAE6.CF12B5C5@mindspring.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3C45EAE6.CF12B5C5@mindspring.com> User-Agent: Mutt/1.3.23i X-Operating-System: FreeBSD cicely8.cicely.de 5.0-CURRENT i386 Sender: owner-freebsd-alpha@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org On Wed, Jan 16, 2002 at 01:04:38PM -0800, Terry Lambert wrote: > Bernd Walter wrote: > > > A real NULL-modem cable looks like: > > > > > > TX -------- RX > > > RX -------- TX > > > CTS -------- RTS > > > RTS -------- CTS > > > GND -------- GND (signal ground, not chassis ground) > > > DCD -------- DTR > > > DTR -------- DCD > > > GND -------- (chassis ground on one end to all other wires) > > > > I usually additionaly bridge DSR with DCD on both sides just in > > case I need to use it for designs requiring DSR. > > I considered that, but these are DTE interfaces, not DCE, so it > makes no sense. > > If I knew it was DTE<->DCE or DCE<->DTE, I would have tied DSR > on one side to DSR and DTR on the other for both sides, per > > Technical Aspects of Data Communications > John McNamara > Digital Press > ASIN: 1555581110 Think of DTE<->DTE with CDSR_OFLOW. It's unusual for Unix systems but some others do. > (I don't know why I always think this was by McKneely; in any > case, for $5 used on Amazon, this is a cheap way to get some > neat information, including the Bell 103 and 202 standards, > which are expensive to get elsewhere). > > As it is, you could end up with +11v <-> +11v, and with the > signal grounds tied and the chassis ground untied, you could > get a ground loop (best case) or cook a TTL chip (worst case, > assuming a multiport chip or multiple connections per pinout > internally). I only see single output connected to one or two inputs. What I meant is (symetric of course): DTR --------o--DSR | `--DCD I havn't thought about using the cable accidantly in a different environment, but fortunately modern interfaces are protected in many ways so the worst case you should get is a non working connection. A simple diode to protect from current backflow and a current limitation on at least one side is all you need to handle this case. -- B.Walter COSMO-Project http://www.cosmo-project.de ticso@cicely.de Usergroup info@cosmo-project.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message