On 29 Oct 99, at 10:08, [log in to unmask] wrote:

> Just over a year ago I purchased an ACER 310S Scanner.  It came
> with an ISA SCSI Card which is working well.  I recently purchased
> an Adaptec 2906 PCI SCSI Card to replace my orginal.  While reading
> thru the manual,  references are made to a SCSI terminator on the
> last external device.  The scanner I have did not come with a
> terminator and does not have one installed.
>
> While looking up the price of a terminator, I discovered a wide
> selection of terminators.   This made me even more confused.
>
> My question is, what type of terminator should I get.  The scanner
> is my only external device.

  Does the scanner have two SCSI ports?  If not, it may have an
internal terminator, and simply must be the last device in any SCSI
chain.

  If there is a second SCSI connector on the scanner, this doesn't
guarantee that it doesn't also have an internal terminator, although
it's much less likely.  Check carefully for any switch or jumper that
might be enabling internal termination.

  Assuming that there is a second connector and no switch/jumper,
it's simply a matter of luck that it has been working so far....
  The *kind* (size and shape) of the connector[*] is going to be the
primary determinant of what kind of terminator you need.  Obviously,
it has to physically fit.
  An "active" terminator is better than a "passive" one -- but also
more expensive.  Active terminators usually include a power-on LED
(usually green, for some reason...).

  "Differential" SCSI uses a different signalling scheme, and a
different kind of terminator.  I don't believe this is likely to
apply to any of the components you've mentioned.


[*] External SCSI connectors may be:

1.  DB-25 -- looks physically the same as a printer port.  Common on
older Macs and Iomega Zip drives.

2.  C50 -- looks like the Centronics connector on a parallel printer,
but with 50 pins instead of the printer's 36.  Also called "SCSI 1".

3.  HD50 -- Looks like a DB-25, but with sharper corners and much
finer pins/spacing.  Also called "SCSI 2".

4.  HD68 -- Looks like HD50, but wider; also called "Wide SCSI" or
sometimes "SCSI 3".  Not likely to be found on a scanner, but you
never know.

David G

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