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From: wilker@gauss.math.purdue.edu (Clarence Wilkerson)
Newsgroups: comp.periphs.scsi
Subject: Re: SCSI cable
Message-ID: <15459@mentor.cc.purdue.edu>
Date: 21 Oct 90 20:34:00 GMT
References: <1990Oct17.022235.22598@tkou02.enet.dec.com> <269@organpipe.UUCP>
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Reply-To: wilker@gauss.math.purdue.edu.UUCP (Clarence Wilkerson)
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One note of caution in making your own cables. The standard numbering
on a DB-50 plug or socket do not match up with the standard 50 line
flat cable clamped to such a socket. To illustrate, the plug may come
marked as ( or mirror image of this )
1  2   3   4  ....    17 ( top row)
  18 19 20 ......         (middle row)
34  35  36.......         (bottom row)

However, if you clamp this onto to a flat cable the correspondence
is more like
DB50      cable
1         1
18        2
34        3
2         4    etc
Fortunately, the female socket on the back of a sun 3/50 is
clamped onto a flat 50 pin cable, so the above change cancels
out the change of pin assignments on the DB50. That is, an even
number of such mappings cancel out in the sense that a flat 50
pin cable at the end will have the standard "scsi" pin assignemnts.
  I'm repeating this because the sun hardware manual is very unclear
on this. In summary, except for pin 26 ??? termination power
questions,  and RFI problems, you should be able to make a working cable by
taking a standard clampon insulation displacemnt type DB-50
male plug, on a 50-wire flat cable on one end, and a 50-pin centronics
connection on the other, if the centronics connector pin connections
are the scsi standard. However, if you are handwiring the cable, do
NOT connect pin x of the DB-50 to pin X of the centronics connector.