Date: Fri, 28 Nov 1997 12:28:55 -0800 From: "Michael L. VanLoon -- HeadCandy.com" <michaelv@mindbender.serv.net> To: dg@root.com Cc: jack <jack@diamond.xtalwind.net>, freebsd-isp@freebsd.org Subject: Re: Adaptec 2940 and FreeBSD 2.2.2-RELEASE Message-ID: <199711282028.MAA02302@MindBender.serv.net> In-Reply-To: Your message of Fri, 28 Nov 97 12:06:42 -0800. <199711282006.MAA19602@implode.root.com>
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>>The trick, I think, is to have the last wide and the last narrow devices
>>terminated. On the controller do not terminate the narrow but do
>>terminate the wide. Works out something like this:
>>
>>
>>W---------------C
>>I O
>>D N
>>E---------------T
>>N---------------r-------N
>>A o A
>>R l R
>>R---------------r-------R
>>
>>Note that you can only use two of internal narrow, internal wide, and
>>external. Using all three results in a 'Y' effect on the narrow side of
>>the scsi chain.
> That would terminate the narrow portion in the middle of the cable for one
>end of the termination. Termination needs to be at the physical end of the
>cable in order for it to work correctly. For people who need to put a narrow
>drive on a wide SCSI bus, there are available special wide->narrow converters
>that provide termination for the upper data bits - they're quite a bit more
>expensive, however.
I can't speak for other controllers, but both the BT94[68] and the
Adaptec 2940(U|UW) allow you to specify the lower and upper byte
termination separately. Meaning, in this diagram, you could disable
lower byte termination on the card, and enable upper byte. That would
properly terminate this scenario.
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Michael L. VanLoon michaelv@MindBender.serv.net
Contract software development for Windows NT, Windows 95 and Unix.
Windows NT and Unix server development in C++ and C.
--< Free your mind and your machine -- NetBSD free un*x >--
NetBSD working ports: 386+PC, Mac 68k, Amiga, Atari 68k, HP300, Sun3,
Sun4/4c/4m, DEC MIPS, DEC Alpha, PC532, VAX, MVME68k, arm32...
NetBSD ports in progress: PICA, others...
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