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From: barr@convex.UUCP
Newsgroups: comp.arch
Subject: Re: VME/68020 Multiprocessor boards
Message-ID: <63900009@convex>
Date: Fri, 6-Nov-87 12:23:00 EST
Article-I.D.: convex.63900009
Posted: Fri Nov  6 12:23:00 1987
Date-Received: Thu, 3-Dec-87 21:49:03 EST
References: <44165@beno.seismo.CSS.GOV>
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Nf-ID: #R:beno.seismo.CSS.GOV:-4416500:convex:63900009:000:1244
Nf-From: convex.UUCP!barr    Nov  6 11:23:00 1987


As far as choice of cpu and controller, you really need to eval-
uate the alternatives based upon the features and performance
required by your particular application.  I was rather surprised
to hear the extreme bias towards Ciprico over Interphase in a
previous posting.  My experience with both companies' SMD disk
products has been good, neither product appears to be "junk".
I'd like to hear grenley@nsc justify that statement with some
performance or reliability numbers.

The choice of backplane is very important.  Be aware that there
is a problem inherent to VMEbus systems that manifests itself
as a noise hit on the bus arbitration lines, and it is most
severe for 32-bit operation.  See the September `86 issue of
DIGITAL DESIGN, "Switching Transients in Microcomputer System
Buses", and the April 30 '87 issue of EDN, "Simple Solution
Cures Glitches on High-Speed Buses" for descriptions of the
problem and some recommended solutions.

Backplanes are available that isolate the A, B, and C signal
rows each in it's own layer with ground plane in between, and
also run ground between each signal trace in a particular layer.
Don't ignore the electrical characteristics of the backplane,
especially in a high-performance application.