Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!uwm.edu!bbn.com!apple!goofy.apple.com!esmith From: esmith@goofy.apple.com (Eric Smith) Newsgroups: comp.sys.mac.hardware Subject: Re: Toshiba XM-3201 and the Mac IIfx Message-ID: Date: 7 Aug 90 23:11:22 GMT References: <65766@coherent.coherent.com> <66179@coherent.coherent.com> Sender: usenet@Apple.COM Followup-To: comp.sys.mac.hardware Distribution: comp Organization: Frobozz Magic Widget Company Lines: 45 In-reply-to: dplatt@coherent.com's message of 7 Aug 90 22:02:35 GMT In article <66179@coherent.coherent.com> dplatt@coherent.com (Dave Platt) writes: 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. If the problem is not noise, ringing, or reflections, does their driver do Macintosh-style "blind reads"? From the description above it sounds as though the problem is in the handshaking. I would think that Using standard (non-blind) accesses would solve this problem, since then standard SCSI-1 handshaking is used. The handshaking is supposed to make SCSI independent of the maximum transfer rate of both the initiator and target. Disclaimer: My job has nothing to do with SCSI. I just have hacked around with it in my copious free time (ha, ha). So I probably don't know what I'm talking about. -- Eric L. Smith Opinions expressed herein do not necessarily reflect those esmith@apple.com of my employer, friends, family, computer, or even me! :-)