From owner-aic7xxx Mon Feb 8 14:47:15 1999 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id OAA18522 for aic7xxx-outgoing; Mon, 8 Feb 1999 14:47:15 -0800 (PST) (envelope-from owner-aic7xxx@FreeBSD.ORG) Received: from mail.blkbox.com (s34.max1.houston.box.net [206.109.96.63]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id OAA18511 for ; Mon, 8 Feb 1999 14:47:12 -0800 (PST) (envelope-from jct@mail.blkbox.com) Received: (from jct@localhost) by mail.blkbox.com (8.8.7/8.8.7) id QAA07848; Mon, 8 Feb 1999 16:49:05 GMT From: Jim Thompson MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Date: Mon, 8 Feb 1999 16:49:04 +0000 (/etc/localtime) To: aic7xxx@FreeBSD.ORG Cc: "'Beau James'" , "Smith, Jeremy" Subject: RE: SCSI bus topology questions In-Reply-To: <61F2369A784ED211B22D00104B59E210800B@bhtriex.mps.bellhowell.com> References: <61F2369A784ED211B22D00104B59E210800B@bhtriex.mps.bellhowell.com> X-Mailer: VM 6.43 under 20.4 "Emerald" XEmacs Lucid Message-ID: <14015.4586.135206.507765@belboz> Reply-To: Jim Thompson Sender: owner-aic7xxx@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org >>>>> "Jeremy" == Smith, Jeremy writes: Jeremy> If I'm not mistaken the disable/enable option is for the Jeremy> low-byte SE terminator on the SCSI bus. This is the only Jeremy> term shared between any of the "plugs". High-Byte UW should Jeremy> always be termed in this setup and High/Low-byte U2W should Jeremy> always be termed. If both of the SE connectors are in use Jeremy> then the Low byte on the bus would not need to be terminated Jeremy> by the host adapter as it is in the middle of the bus. The Jeremy> Low byte should be terminated with good quality terminators Jeremy> on either end of the SE bus. Often times the terms on Jeremy> CD-ROMS, tape drive and the like are not of very good Jeremy> quality. Try disabling the terminator in the SCSI Bios and Jeremy> if that fails get a couple of active terminators to put on Jeremy> the ends of your cables. Let me second Beau's original plea -- I find the P2B-S termination to be terribly confusing. Perhaps the way to understand it is to turn the question around: if I have devices on each of the three bus segments (LDV, wide-SE, narrow-SE), then: (a) does the last device on each bus segment need to be terminated? (b) what termination, if any, needs to be enabled on the motherboard? Presumably, the answer to (a) would be "yes". Each cable has a *physical* end, which needs to be terminated to keep signals from bouncing from it. The answer to (b) is what's confusing, and seems to rely on some assumptions about what's electrically connected to what at the motherboard (SCSI controller). If the narrow and wide SE segments are electrically tied together, then the answer would seem to be "high on, low off". To add to the confusion, both the Award and Adaptec BIOSes have termination settings. The Award BIOS two on/off termination settings, one for high, one for low. The Adaptec BIOS has only one one/off setting, simply labeled "termination". JT -- _ | .~. _| ~- Jim Thompson | Yo quiero Linux /V\ \, _} jim.thompson@pobox.com | /( )\ \( http://pobox.com/~kzinti | ^-^ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe aic7xxx" in the body of the message