Path: utzoo!attcan!uunet!husc6!think!ames!vsi1!wyse!mips!sultra!dtynan
From: dtynan@sultra.UUCP (Der Tynan)
Newsgroups: comp.sys.m68k
Subject: Re: VME <=> PC bus
Summary: Brain-dead bus structure.
Message-ID: <2562@sultra.UUCP>
Date: 7 Oct 88 22:58:57 GMT
References: <363@babbage.acc.virginia.edu>
Organization: Tynan Computers, Sunnyvale, CA
Lines: 27

In article <363@babbage.acc.virginia.edu>, Alex Colvin writes:
> Is there a device available to link a PC bus to a VME bus?
> I have a PC that I'd like to make a peripheral on the VME bus.
> 
> If I can't share memory among the machines, is there a fast, simple,
> short-haul link?  I'd rather not use a 2.5 meter ethernet.

Sorry to have to post this, but vnews core-dumps when I try to reply (some
incentive not to post, huh?).  Unfortunately, the IBM-PC bus is pretty
stupid, when it comes to things like this (I know, I know, don't send me a
lot of mail about what the designers motivation was, it's still dumb!).

The problems are numerous.  The biggest, is that you can't address INTO the
PC box.  The address drivers are unidirectional, and cannot be tristated.
Thus, the PC could possibly see your VME box, but not vice-versa.  There are
other problems that I won't go into unless someone else is interested, but
all-in-all, it's not easy.

Of course, this isn't really what you asked, so a direct answer to your
question;  1/  I don't know of any hardware to do it.  2/  The ethernet
is the most elegant solution -- that way, you also get an ethernet link,
if you ever get another system.  What's wrong with a 2.5m ethernet?
						- Der
-- 
Reply:	dtynan@sultra.UUCP		(Der Tynan @ Tynan Computers)
	{mips,pyramid}!sultra!dtynan
	Cast a cold eye on life, on death.  Horseman, pass by...    [WBY]