On Mon, 14 Feb 2000, Irv Thomae wrote:
> On Mon, 14 Feb 2000 07:00:29 -0800, Andrew McHorney wrote:
>
> >Well I can get a simple 4 to 6 scsi foot cable for now. When I get my
> >computer desk setup, the scanner will be located much closer and then I can
> >use a 3 foot cable.
> >
> >The scanner came with an adaptec controller which is ok, but I would rather
> >not waste a slot.
> >
> >Andrew
> >
>
> Although it's certainly true that a decent SCSI controller can accept a wide
> mix of devices insofar as addressing and delivery are concerned, OTOH it's also
> true that slow devices can limit bus speed, effectively bringing all down to
> the "least common denominator". *That*, IMHO, is a strong argument for using a
> distinct (low-speed, cheap) controller for your scanner. Also, with a lower
> maximum speed, the separate bus will more easily tolerate the 6-foot cable
> length.
> Didn't an el-cheapo controller come with the scanner? If not, check
> misc.forsale.whatever , a likely place to find people with extra hardware they
> don't happen to want....
This is in fact the real nub of the matter. Mixing slow devices and fast
devices on the same bus is really going to cause more problems than it is
worth. As far as I know the majority of scsi scanner don't allow the
DISCONNET command for suspending data transfers while other devices access
the bus. That coupled with the higher tolerances you'll need for a 6ft
long termination (ie completely active and all devices supplying power, if
they can) then it really becomes a headache.
I am sure there are plenty of SCSI gurus out there who can explain
to you the limitations of bandwidth between fast busses and slow & fast
devices. Personally I have gone the whole hog and use a 4 channel
(APB3980UA) controller and seperate out HD's , TAPE/DAT's, CDROM/CDRW's
and the
scanners (I have 2) onto seperate channels grouping the slowest together
and the fastest to make the maximum use of the available bandwidth. Oh
incidentally before I got this controiller I had the trusty ol' 1542CP and
a APB960 working together. It ran like a dream :)
Hope this helps, you never know it might even work out cheaper
than an exotic 68->25 cable ;)
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