From owner-freebsd-alpha Wed Jan 16 13: 4:57 2002 Delivered-To: freebsd-alpha@freebsd.org Received: from avocet.prod.itd.earthlink.net (avocet.mail.pas.earthlink.net [207.217.120.50]) by hub.freebsd.org (Postfix) with ESMTP id 2F50F37B416 for ; Wed, 16 Jan 2002 13:04:53 -0800 (PST) Received: from pool0454.cvx21-bradley.dialup.earthlink.net ([209.179.193.199] helo=mindspring.com) by avocet.prod.itd.earthlink.net with esmtp (Exim 3.33 #1) id 16QxEe-0001nK-00; Wed, 16 Jan 2002 13:04:41 -0800 Message-ID: <3C45EAE6.CF12B5C5@mindspring.com> Date: Wed, 16 Jan 2002 13:04:38 -0800 From: Terry Lambert X-Mailer: Mozilla 4.7 [en]C-CCK-MCD {Sony} (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Bernd Walter Cc: Trevor Johnson , Riccardo.Veraldi@fi.infn.it, freebsd-alpha@FreeBSD.ORG Subject: Re: DEC3000/300 References: <20020116023458.E17814-100000@blues.jpj.net> <3C45DF84.5990A4E4@mindspring.com> <20020116214931.M50371@cicely8.cicely.de> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit 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 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 (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). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message