SCSI Cable Weirdness

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Article #13585

#13585

From: ephraim
Date: Fri, 21 Nov 1986 13:15

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Here's a problem you might meet if you're building your own SCSI
cable.  The Apple connector has 25 pins, a "real" SCSI connector has
50.  All the odd SCSI pins are ground, so you might suppose that the
easy thing to do is match up the 25 Apple pins with the 25 even
SCSI pins (which include about 5 grounds and one NC), ignoring all
those odd pins.  If you do, your cable might or might not work.

On some controllers, the manufacturer cheated with the even-numbered
SCSI grounds: They're not connected!  So, if you only use the even
pins, your cable might not have any ground at all in it.  The fix
is to tie all the Apple grounds to *odd* SCSI pins.  These really
are grounded on every controller I've seen.

Sadder but wiser,
Ephraim Vishniac
decvax!wanginst!wang!ephraim

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Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: arc1-ca.pugleaf.net!utzoo!watmath!clyde!rutgers!ll-xn!mit-eddie!genrad!decvax!wanginst!wang!ephraim
From: ephraim@wang.UUCP
Newsgroups: comp.sys.mac
Subject: SCSI Cable Weirdness
Message-ID: <1638@wang.UUCP>
Date: Fri, 21-Nov-86 08:15:32 EST
Article-I.D.: wang.1638
Posted: Fri Nov 21 08:15:32 1986
Date-Received: Sun, 23-Nov-86 02:59:37 EST
Distribution: net
Organization: Wang Labs, Lowell MA
Lines: 16