From owner-freebsd-hardware Sun Nov 3 23:55:03 1996 Return-Path: owner-hardware Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id XAA04156 for hardware-outgoing; Sun, 3 Nov 1996 23:55:03 -0800 (PST) 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 XAA04146 for ; Sun, 3 Nov 1996 23:54:59 -0800 (PST) Received: (from rgrimes@localhost) by GndRsh.aac.dev.com (8.7.5/8.7.3) id XAA03238; Sun, 3 Nov 1996 23:54:48 -0800 (PST) From: "Rodney W. Grimes" Message-Id: <199611040754.XAA03238@GndRsh.aac.dev.com> Subject: Re: OK, what's the deal with 2940W controllers and internal connectors? In-Reply-To: <199611040242.SAA00127@freefall.freebsd.org> from "Justin T. Gibbs" at "Nov 3, 96 06:42:33 pm" To: gibbs@freefall.freebsd.org (Justin T. Gibbs) Date: Sun, 3 Nov 1996 23:54:47 -0800 (PST) Cc: jkh@time.cdrom.com, 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 > According to Adaptec, you are supposed to use only two or the three you CAN use ANY two OF the three connectors... > connectors on the card. I'm sure the EE members of the crowd can > tell you why. All three connectors on the card are electrically and MECHANICALLY within the ``stub'' length allowed by the SCSI spec, thus you don't have a Y (as some one else put it) as long as you only use 2 of the 3 connectors. The SCSI spec allows a small unterminated stub to exists on the SCSI bus. Your 2940UW looks something like this: XW--IW--IN XW is the eXternal Wide connector, IW is the Internal Wide connector, IN is the Internal Narrow connector, and -- is a very short distance. Now as you can see: XW--IW--IN | | | ---------ND WD When we add drives using both internal connectors we have this little stub bus out to the XW connector, no big deal, the SCSI spec allows it. Note that the 2940UW must terminate ONLY the high 8 bits of the wide bus in this configuration, and both WD and ND must be terminated. Other configurations can be found in the manuals, and as usual termination configuration is left as an excercise to the user... -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation, Inc. Reliable computers for FreeBSD