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From: dplatt@coherent.com (Dave Platt)
Newsgroups: comp.sys.mac.hardware,comp.periphs.scsi
Subject: Re: Toshiba XM-3201 and the Mac IIfx
Message-ID: <66179@coherent.coherent.com>
Date: 7 Aug 90 22:02:35 GMT
References: <65766@coherent.coherent.com>
Reply-To: dplatt@coherent.com (Dave Platt)
Followup-To: comp.sys.mac.hardware
Distribution: comp
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 62

In article <65766@coherent.coherent.com> I wrote:

> The consensus: at the moment, the XM-3201 does _not_ work reliably with
> the IIfx.

Since I posted the above note on Friday, I've had a long and fruitful
conversation with one of Toshiba's CD-ROM hardware gurus, and a shorter
and equally fruitful conversation with one of OMI's software developers.

What I learned is as follows (quotations below summarize what I was
told;  they are not exact):

-  The Toshiba XM-3201 CD-ROM drive does indeed have some problems
   working with the Macintosh IIfx.

-  The problems are due to the high speed of the IIfx SCSI chip... the
   IIfx is overrunning the CD-ROM drive processor somehow.  The problem
   affects the XM-3201 model, and I'm told that some hard-disk
   manufacturers have had similar problems with their drives.  "The IIfx
   SCSI implementation is much faster than anything we've seen before."

-  The problem is _not_ due simply to electrical noise, ringing, or
   reflections on the SCSI bus (due to improper termination of the bus,
   incorrectly-wired cabinets which create unterminated "stubs" on the
   bus, etc.).  The problem can show up even if the bus is wired and
   terminated according to the SCSI-1 specifications, using a Mac IIfx
   terminator at the far end of the bus, and is electrically "clean" as
   shown by a TDR analysis.

-  It's possible to work around the problem by installing a long SCSI
   cable between the Mac IIfx and the XM-3201.  This apparently
   introduces enough delay into the SCSI bus to keep the XM-3201
   controller from being swamped.  "8 feet of cable usually
   works;  go for 10 or 12 feet if you can.  The long cable must be
   between the Mac and the drive... putting the long cable on the far
   side of the drive won't help.  10 feet of ribbon cable, folded back
   and forth in a box, with a 'D' connector on each end, is one way to
   do it.  I wouldn't call this a 'fix'... more of a 'band-aid'... but
   it does seem to work."

-  Toshiba is looking into better solutions for the problem.  It's
   uncertain whether they'll choose to update the XM-3201 hardware to
   support the IIfx... a circuit modification has been developed, but in
   its current form it's not easy to install and won't allow the drive
   cover to fit back into place.  Toshiba might decide to wait for the
   next model (XM-3300 series) to come out, and make sure that this new
   design will work correctly with the IIfx.  "It's really a matter
   between the marketing people here, and the technical people in Japan.
   Our relationship with the manufacturing-and-design people in Japan is
   similar to that of a big O.E.M."

-  Either version 1.2, or version 1.3.1 of the Toshiba driver (OEM'ed
   from OMI) should work OK with the IIfx.  Version 1.3 might not mount
   discs properly.

So... if you have a CD-ROM drive which uses the Toshiba mechanism, you
can probably use it with a IIfx by installing a long SCSI cable.  It's
not an ideal solution, but anecdotal reports suggest that it does work.

If you have a IIfx and are thinking of buying a CD-ROM drive based on
the Toshiba mechanism, you might want to make sure that you can return
the drive for credit if it doesn't work properly with your IIfx.