🚀 go-pugleaf

Submitted for the FAQ:

QUESTION: I have an Adaptec 2940W (2940UW), a wide internal disk drive,
a regular SCSI 2 internal CD-ROM, and a SCSI 1 external SCSI device
(tape, ZIP, whatever).  How do I cable these together?

ANSWER:

The Adaptec AHA-2940W and AHA-2940UW SCSI host adapters have three
cable headers: an internal 68-pin "Wide" header, an internal 50-pin
"SCSI 2" header, and an external 68-pin "Wide" or "SCSI 3" connector.
The retail and oem packages include two internal cables: a three
connector (2 device) 68-pin "Wide" cable, and a three connector (2
device) 50-pin cable.

The obvious thing to do would be to buy a 68-pin to HD-50 or
Centronics-50 external cable (whatever your external device needs), and
just cable up each device to the obvious connector: the internal wide
drive to the 68-pin header, the internal CD-ROM to the 50-pin header,
using the supplied internal cables, and the external device with the
external cable.

Guess what?  That won't work.  It says in the Adaptec documentation
that you CANNOT USE ALL THREE CABLE HEADERS SIMULTANEOUSLY.  Proper
SCSI cabling requires a single, logical straight line cable path with no
Y's or T's, with termination at both ends of the path.  Using all three
connectors on the Adaptec would create a Y, with the adapter card in
the middle.  Also, using all three connectors would create three
termination points, also a no-no.

The upshot is that you have to limit yourself to using no more than 2 of
the 3 connectors at any time.  Since you have an external device, you
have to use the external connector.  Since you have a wide disk drive,
you have to use the internal 68-pin Wide connector.

What do you do with the internal 50-pin CD-ROM?

You need to buy the following connector from Adaptec:

	ACK-68p-50p-I Converter			$25

This will convert the 50-pin male header on your CD-ROM (or other
internal narrow SCSI device) into a 68-pin female header, appropriate
for the 68-pin cable.

SCSI allows wide or narrow, fast or slow devices to be on the same
cable, but you still have to worry about proper termination.

IMPORTANT: When mixing wide and narrow devices on a wide cable, the
cable MUST BE TERMINATED BY A WIDE DEVICE.  Just make sure that the last
device on the physical cable is a wide device, and that it provides
termination for that end of the bus.

Why do I know all this?  I had to figure it out, since I have a Pentium
that needs three SCSI devices just as I've described above.  It took
several days, lot's of searching, and a lot of waiting on hold at
Adaptec's complementary tech support line to get the answers.  Why
should you have to go through all that too?

You can also get an external connector from Adaptec to convert the
external 68p female connector to an HD-50 pin female plug
(ACK-68p-50p-E).

Perry

-- 
caro@mv.us.adobe.com  ...!{sun}!adobe!caro   Contents: my opinions, no others