Date: Sun, 24 May 98 23:54:00 -0000 From: mikebw@bilow.bilow.uu.ids.net (Mike Bilow) To: aic7xxx@FreeBSD.ORG Subject: Adaptec termination problem... Message-ID: <568a4e82@bilow.bilow.uu.ids.net>
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Grover Davidson wrote in a message to Mike Bilow: GD> I could be WAY out on this, but if memory serves me right, GD> the device that is FARTHEST away from the controller should GD> be terminated, regardless of its address. Termination, GD> preferably ACTIVE termination, belongs at the far end away GD> from the controller. Otherwise, the electrical GD> charictaristics that termination is designed to achieve GD> don't occur. Generally, yes. There are complications when you switch the bus midway from wide to narrow, which happens on the 2940xW, but the principle is right. GD> I have a 2940W with: GD> 0:IBM Starfire 4.5GB Fast/Wide GD> 1:Conner 540MB Fast GD> 2:Syquest 270MB GD> 4:IBM 8x CdRom (from an RS-6000) GD> 6:Exabyte 8200 8mm tape drive GD> My Wide cable has 1 activer terminator on it at the far end, GD> and my IBM drive is also plugged in at the far end. GD> My narrow bus has things plugged in in the order listed with GD> the higher addresses being farther from the contoller. My GD> termination on the narrow bus is supplied by the Exabyte GD> with passive termination. In your configuration, the controller is the physical end of the high half of th wide bus, but is in the physical middle of the low half of the wide bus which is also the whole narrow bus. As a result, the correct configuration is for the controller to terminate the high half but not the low half, and then the wide and narrow devices physically farthest from controller are terminated. GD> I have never had a problem with that layout. I have know a GD> lot of people who have had problems with their scsi system, GD> and about 90% of those were due to impropper termination. It sounds as if you did it right. If the bus is underterminated, this will cause ringing that will result in data errors, parity errors, and possibly even lockups. If the bus is overterminated, it will usually work, but will support less than the rated number of peripheral devices. -- Mike To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe aic7xxx" in the body of the message
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