From owner-freebsd-current@FreeBSD.ORG Fri Jul 18 00:28:08 2003 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id C19CB37B401 for ; Fri, 18 Jul 2003 00:28:08 -0700 (PDT) Received: from heron.mail.pas.earthlink.net (heron.mail.pas.earthlink.net [207.217.120.189]) by mx1.FreeBSD.org (Postfix) with ESMTP id 31D8D43F3F for ; Fri, 18 Jul 2003 00:28:08 -0700 (PDT) (envelope-from tlambert2@mindspring.com) Received: from user-2ivfi0c.dialup.mindspring.com ([165.247.200.12] helo=mindspring.com) by heron.mail.pas.earthlink.net with asmtp (SSLv3:RC4-MD5:128) (Exim 3.33 #1) id 19dPev-00048R-00; Fri, 18 Jul 2003 00:28:06 -0700 Message-ID: <3F17A143.E4C80A40@mindspring.com> Date: Fri, 18 Jul 2003 00:26:59 -0700 From: Terry Lambert X-Mailer: Mozilla 4.79 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Harald Schmalzbauer References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-ELNK-Trace: b1a02af9316fbb217a47c185c03b154d40683398e744b8a4d2c15bca579b15c6fde87f7cf754c6ce93caf27dac41a8fd350badd9bab72f9c350badd9bab72f9c cc: freebsd-current@freebsd.org Subject: Re: HPT372 bug summary [was: RE: escalation stage 2] X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Jul 2003 07:28:09 -0000 Harald Schmalzbauer wrote: > Please forget that. It was because for convinience reasons I had turned the > 80-pin ATA cables upside down. So the black was at the controller and the > blue at the drive. > I can't imagine that this makes any technical difference (as long as no > slave drive is connected and there's no open end) > But it seems the single connectors are electrical coded (again I can't > imagine how?!?) >From the "Computer Lore For What It's Worth" department... In cables with free wires in them, it's very common to ground them on only one ends of the cable (usually, the end with the best chassis ground, which in this case would be the host), so that the free wires act to damp noise in the environment from effecting the other lines... basically, a Farraday cage. It's very common to see this in old RS-232C cables, as well as in SCSI cables, especially the long ones used in differential SCSI, if they don't have shielding. The reason you connect only one end is to avoid ground loops, which you can get if you use line voltage base reference: for example, on RS-232C, it was common to abuse the standard and send a digital ground of 12 volts on the digital ground as the zero voltage base reference, which gave you -11 (= +1) and +11 (= +23) for 24v telephone equipment, so that you didn't have to have a power supply capable of putting out -11v and regulate the +24 to +11. If the cable cared, it probably cared because it was grounded on the host side and not on the drive, and the drive probably didn't hook the pins up at all, to avoid ground loops when using cables that *did* connect the pins through. Best case, you were connected to digital instead of chassis ground on the drive side, and worst case, you were unconnected on the host end *and* the drive end, and so had a nice big linear capacitor/dipole antenna. 8-). In other words, if a cable says to connect it a specific way, there's probably a good reason. -- Terry