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From: jbn@wdl1.UUCP
Newsgroups: net.micro.68k
Subject: Re: Multiple 68020's on VME ?
Message-ID: <729@wdl1.UUCP>
Date: Mon, 30-Sep-85 20:59:49 EDT
Article-I.D.: wdl1.729
Posted: Mon Sep 30 20:59:49 1985
Date-Received: Thu, 3-Oct-85 06:36:02 EDT
Sender: notes@wdl1.UUCP
Organization: Ford Aerospace, Western Development Laboratories
Lines: 22
Nf-ID: #R:rna:-44200:wdl1:22700016:000:898
Nf-From: wdl1!jbn    Sep 30 17:57:00 1985


      We have a system with several bus masters on one VMEbus, and ran into
the following problems:

	1)  The Omnibyte CPU card incorrectly performed its slot 1 bus
	    arbitration function, due to a problem with the Motorola
	    bus arbiter chip.  Omnibyte replaced the chip with a small
	    daughter board with two chips, which fixed the problem.

	2)  The Ironics RAM card was discovered to raise DTACK before it
	    was done with the data; as long as the cycle came from a
	    M68000 this was OK, because the M68000 kept the lines up just
	    long enough for it to work, but our own DMA peripheral didn't
	    and the RAM board would write bad parity into memory.  No fix;
	    we've switched to DY-4 RAM cards.

Moral: ask your board vendor ``Have you run this thing with multiple bus
masters?''  Both these cards work beautifully until you put on the second
bus master.

				John Nagle