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Date: Sun, 03 Nov 1996 22:17:31 -0600
From: Alex Nash <nash@mcs.com>
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To: "Jordan K. Hubbard" <jkh@time.cdrom.com>
CC: hardware@freebsd.org
Subject: Re: OK, what's the deal with 2940W controllers and internal connectors?
References: <8387.847074260@time.cdrom.com>
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Jordan K. Hubbard wrote:
> I just recently had a WIDE drive fall into my lap, so I finally
> started putting that WIDE connector on my 2940UW controller to good
> use.  While reading the Adaptec controller docs before jumping in, I
> saw that it very specifically said to use only ONE of the internal
> connectors, either the WIDE or the narrow, but not both.  You could
> still use the external connector for either kind of drive, but not
> hook both internal connectors up at once.  Well, this made sense to me
> since it seemed like otherwise you'd have a "Y" configuration in your
> SCSI bus, and it wasn't clear which devices you'd terminate if you
> plugged both internal connectors in - each end of the Y, or what?

This is perfectly legitimate, I run such a configuration here.  You
essentially have the following (excuse the poor quality ASCII art):

     Wide Devices                 Narrow Devices
       low bits  !-------+------------!
                        2940
       high bits !-------!

Where '!' indicates termination points.  In the Adaptec BIOS, you'll
see termination options for low on/off and high on/off.  These refer
to whether or not the adapter is terminating those bits of the bus.
For devices on the wide and narrow busses, you want high on/low off.
The low bits are being terminated by the wide and narrow devices,
whereas the high bits are only terminated on the wide bus.

Alex