From owner-freebsd-hardware Fri Oct 25 08:14:50 1996 Return-Path: owner-hardware Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id IAA25813 for hardware-outgoing; Fri, 25 Oct 1996 08:14:50 -0700 (PDT) Received: from GndRsh.aac.dev.com (GndRsh.aac.dev.com [198.145.92.241]) by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id IAA25806 for ; Fri, 25 Oct 1996 08:14:44 -0700 (PDT) Received: (from rgrimes@localhost) by GndRsh.aac.dev.com (8.7.5/8.7.3) id IAA10037; Fri, 25 Oct 1996 08:13:49 -0700 (PDT) From: "Rodney W. Grimes" Message-Id: <199610251513.IAA10037@GndRsh.aac.dev.com> Subject: Re: Setting up an actively terminated SCSI chain. In-Reply-To: <199610250620.PAA18255@genesis.atrad.adelaide.edu.au> from Michael Smith at "Oct 25, 96 03:50:48 pm" To: msmith@atrad.adelaide.edu.au (Michael Smith) Date: Fri, 25 Oct 1996 08:13:49 -0700 (PDT) Cc: msmith@atrad.adelaide.edu.au, sysseh@devetir.qld.gov.au, hardware@freebsd.org X-Mailer: ELM [version 2.4ME+ PL25 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hardware@freebsd.org X-Loop: FreeBSD.org Precedence: bulk > Rodney W. Grimes stands accused of saying: > > > > All correct except for one small detail, also make sure the baracuda is > > suppling termination power on it's own. It is best to have the term > > power supplied by the closests device since term power over the scsi > > cable will invariable have noise on it caused by mutual induction > > and capacitative coupling in the cable itself. > > Heh, I must be getting better then 8) I answered that one in some > follow-on mail on the subject - I should have mentioned it up front. > > Personally though I'd have been more worried about the inductance of the > relatively thin wire in the ribbon than mutual inductance, given that > there are ground conductors either side of TERMPWR. Regardless, it's > the best way to go. Acually your right again, the series inductance of TERMPWR would have far more effect on the stability of an active termination regulator as the current load changes than any noise coupled via mutual inductance. Hummm... maybe we had better move this to some ``ee'' mail list, and run a few spice jobs to see just what 6 feet of 26 awg strip line ribbon cable does to the TERMPWR signal when you draw the current for an active terminator regulator at the end of it and switch the data bus rail to rail...... :-) Anyone have a good strip line model for spectra cable???? -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation, Inc. Reliable computers for FreeBSD