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Subject:
From:
David Gillett <[log in to unmask]>
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Date:
Tue, 3 Feb 1998 16:16:55 -0800
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On  3 Feb 98 at 14:29, Rick Fogel wrote:

> I have an Advansys 940u scsi card and an internal phillips cdd2600
> cd-r insatlled on my computer . It is a pent.166mmx running win 95.
> Everything is finally working here but when i tried to hook up my
> Artec Viewstation scanner it will not recognise it. The scanner is
> set to device 6 and the cd-r is set for 2.

> I was told this card is self terminating. Do i still need to
> terminate the scanner?

  The SCSI bus needs to be terminated at both ends.  If you've got
devices off both the internal and external connectors of the card,
the card is not at an end of the bus, and so should not be providing
termination.
  Therefore, yes, you will need to terminate the scanner.

> I have tried to find a terminator with no success.

  Terminators come in "Active" and "Passive" varieties, and in CN50,
HD50 and HD68 connectors.  [I haven't seen one in DB25, but they
might exist.]  Active terminators seem overpriced to me -- I wouldn't
think you'd need one for just 2 devices (besides controller).
[Actually, it appears that active termination stays reliable as the
bus length increases, which isn't directly related to the number of
devices on the bus.]
  Any place that sells SCSI controllers or drives should be able to
come up with them.

  There's a catalog of SCSI cables and terminators at

  http://www.connectronics.com/scsi.htm

No online ordering setup, but they give a phone number and probably
do mail-order.  [And their price for an HD50 active terminator is
about HALF of what I've seen some places.]

> Can i make one?

  I suppose this must be possible, but I haven't seen any of the
above connectors as a retail item; nor have I seen a wiring diagram.

> Can i use just another scsi cable hooked to the scanner as a
> terminator?

  No, that's not going to do it.  Termination isn't just looking for
something to be plugged in; it wants specific electrical connections
between pins which, in a cable, are isolated from each other.

[http://www.glyphtech.com/glscsifq.htm:  If you have an Ohm-meter of
one kind or another, measure the resistance from the TERMPWR pin to
an adjacent GROUND pin. Reverse the probes and take another reading.
If the reading is about 30.5 Ohms, with the probes both ways, you
have a passive single-ended terminator.  If the reading is about 45
Ohms, with the probes both ways, you have a passive differential
terminator. Active terminators should read much higher and give very
different readings with the probes interchanged.]

David G

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