Newsgroups: comp.periphs.scsi
Path: lth.se!sunic!mcsun!uunet!milo!harry
From: harry@verdix.com (Harry Zint)
Subject: interconnecting cables
Message-ID: <1992Aug24.130058.20106@verdix.com>
Organization: Verdix Corp.
Date: Mon, 24 Aug 1992 13:00:58 GMT
Lines: 49


I recently purchased a new '386 PC.  Because I have a Sun3 "shoe box" with a 
SCSI disk and SCSI tape drive, I outfitted my new PC with a SCSI controller in 
lieu of other possible controller types.

My SCSI controller has an internal 50 pin connector for ribbon cable and an
external 25 pin DB connector for external SCSI devices.  I have an internal
hard disk attached to the controller via the 50 pin connector and the Sun3 
"shoe box" connected via the external 25 pin DB connector.

Because the Sun3 "shoe box" has a 50 pin DB connector, I fabricated a 25 wire
cable having a 25 pin DB connector on one end and a 50 pin DB connector on the
other so I could use the external connector on my SCSI controller.  To 
fabricate this cable, I purchased a 25 wire serial cable, chopped the 25 pin
connector off one end, and grafted a 50 pin connector to the severed end of 
the serial cable.

This fabricated cable works fine for simple SCSI operations like initializing
the device and transferring short bursts of data.  If I try to transfer large
chunks of data like copying 50 meg of files from the PC internal disk to the 
Sun3 "shoe box" disk, the system hangs after transferring an arbitrary amount 
of data.  I have verified that the termination resistors are installed 
correctly.

If I connect the Sun3 "shoe box" to the SCSI controller internal connector 
using a 50 wire ribbon cable, data transfers to the Sun3 "shoe box" work fine.  
In my opinion there is some kind of difference between my fabricated cable and 
the ribbon cable that effects SCSI performance.

It seems to me that there are at least three solutions that could fix the 
problem:
   1. Find a SCSI cable with a 50 pin DB connector on one end and a 
      25 pin DB connector on the other end.  This cable must also be pin 
      for pin compatible with my SCSI controller and Sun3 "shoe box".
   2. Find a 50 pin to 25 pin DB adapter for either the controller or the 
      Sun3 "shoe box" and use either a 25 wire or a 50 wire SCSI cable as
      appropriate.
   3. Find/fabricate a 50 pin DB to 50 pin Centronics adapter.  To work with 
      SCSI cables that are available to me.

I am told Apple Macintosh uses a cable with a 25 pin DB connector on one end 
and a 50 pin DB connector on the other end.  All I can find are SCSI cables 
with a 25 pin DB connector on one end and a 50 pin Centronics on the other end.

Can anyone suggest a reliable and economical solution?

Thanks

harry
