SUMMARY: External narrow SCSI devices on fas0:

From: Thomas Leitner (
Date: Sun Oct 25 1998 - 12:59:35 CST


The consensus is to use an adapter with a terminator on the high
bus. Thanks to the following people for their replies:

Patrick L. Nolan <pln@egret1.Stanford.EDU>
David L. Markowitz <>
Chris Marble <>
Harvey Wamboldt <>

I hope I didn't forget anyone. I'm attaching their replies below along
with my original question.

Thanks again // Tom

From: Patrick L. Nolan <pln@egret1.Stanford.EDU>

I have a situation which I think is similar to yours. I mixed wide and
narrow devices on a fas. Mostly it worked, but there were too many failures
to be acceptable. We bought a second interface, but it's an isp, not
a fas. I don't know anything about the difference. Currently all the
narrow devices are connected happily to the isp. When we bought it we also
got a "High-9 active terminator" to deal with the proper termination of
the 8 unused lines. This is item 5216 in the catalog of UltraSpec Cables
( $60 US.

From: David L. Markowitz <>

You should use a wide-to-narrow cable with high-9 termination. You
probably don't really need one, since there are no wide devices on the
bus, and you can tell the fas driver to not use wide, but do it right. :-)
You never know when you might wish to add a wide device.

You may have had trouble because you had Centronic-style connectors.
Always use the high-density connectors if you can.

Several vendors would be happy to sell you this cable. I recommend
Adaptec, C.S. Electronics, and Ultra Spec, but I'm not sure who you
should contact in Austria.

From: Chris Marble <>

I would think that you could use any 50-68 pin adaptor. Make sure you've
got a good active terminator at the end of your chain.
I've got wide disks on Sun's version of the same card. Had no problems.

-- - HMC UNIX & Information Systems Manager
  My opinions are my own and probably don't represent anything anyway.

------------------------------------------------------------------------- From: Harvey Wamboldt <>

Sounds like you need a wide to narrow terminating adapter ... check out:


However, this only works if your SCSI controller follows the SCSI spec, see below for more...

>From the SCSI FAQ:

==== QUESTION: Can I connect a WIDE device to my narrow SCSI host adapter? QUESTION: Can I connect a narrow device to my WIDE SCSI host adapter? ANSWER FROM: Gary Field ( ====

Yes, you just need an appropriate adapter. Most WIDE devices use the 68 pin "P" connector so you need a 68 pin to 50 pin adapter. You do need to make sure that both the upper byte and lower byte of the bus will be properly terminated though. Some adapters provide a place for terminators, others do not. If the wiring adapter is placed right at the SCSI host adapter, you can usually configure the host adapter's on-board terminators to only terminate the high byte. You need to be clear on what type of connectors are present where you want to do the conversion. You also need to plan your bus so that all the WIDE devices will be at one end and all the narrow devices will be at the other end.. Certain host adapters with auto-termination make the assumption that when the low byte is terminated the high byte is also. When using WIDE/narrow adapters this assumption is not valid. One further caveat is that if narrow devices are attached to a WIDE adapter, the adapter's ID must be between 0 and 7 because narrow devices would not be able to see it if the ID was any higher than 7.

Such adapters are available from:

Technical Cable Concepts 1790 E. McFadden Ave. Unit 103/104 Santa Ana, CA 92705 TEL: (714) 835-1081 FAX: (714) 835-1595

MegaHaus 2201 Pine Drive Dickinson, TX 77539 E-Mail Order Line 800-786-1157 Fax Line (281)534-6580 Main Line (281)534-3919

Dalco Electronics P.O. Box 550 275 South Pioneer Blvd. Springboro, OH 45066-1180

Warning: I am told that some 68 pin to 50 adapters have TERMPWR wired incorrectly such that some of the 4 TERMPWR lines on the 68 pin connector get connected to the pin opposite TERMPWR on the 50 pin side. This pin was originally a GROUND signal and was later changed to OPEN to prevent shorting TERMPWR if the connector was reversed. Also some of these TERMPWR lines might be connected to the RESERVED pins adjacent to TERMPWR. Some drives interpreted RESERVED to mean "OK to connect to GROUND" and therefore attaching one of these will also short out TERMPWR. The proper wiring is for all 4 TERMPWR lines on the 68 pin side to connect to the one TERMPWR line on the 50 pin side and leave the RESERVED lines not connected.

------------------- o r i g i n a l p o s t i n g ---------------------

> We have an Antares combi S-Bus card with a hme0 and a fas0 interface in > an SS20. I did not use the fas0 in the past. Now as we need to add > more harddisks and the standard SCSI bus is already very long, I want > to connect some external narrow SCSI devices to fas0. There is *no* > internal device connected to this fas0 (this ain't possible anyway, IMHO). > > I remember that I already made one attempt to do so with a wide > SCSI 68pin to narrow SCSI 50pin, Centronics adapter cable. Though this > attempt failed miserably. The adapter cable apparently had no terminator > for the upper (unused) bus half, or something. > > So to avoid purchasing something totally wrong: Can anyone tell me > exactly what SCSI adapter cable or SCSI adapter I need to connect > external narrow SCSI devices to a fas0 without an internal device? > > Thanks a lot // Tom

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