Path: utzoo!attcan!telly!lethe!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: 68030 In a Lucas and MMU stuff
Message-ID: <16679@cbmvax.commodore.com>
Date: 19 Dec 90 18:42:05 GMT
References: <1990Dec17.204644.22516@isc.rit.edu>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 56

In article <1990Dec17.204644.22516@isc.rit.edu> smc8516@ultb.rit.edu.isc.rit.edu (S.M. Curtin) writes:

>A friend and I are planning to build LUCAS boards for ourselves within
>the next few months. I seem to remember reading here that one could
>replace the 68020 in a LUCAS with a 68030 providing he rewires the
>socket (and changes it?) and ties off the extra 68030 lines. Is my
>memory correct on this matter. If so, could someone please repost or
>point me in the direction of the pertinent information.

I don't know where they documented it, but in general, a 68030 with a few lines
tied off is a drop in replacement for the 68020.  The pinout is, of course,
different and must be adjusted for, but the timing is virtually identical.  Off
the top of my head, you need to pull up the STERM*, CIIN*, CBREQ*, and 
MMUDIS* lines, all others should have 68020 equivalents or are unused outputs.

>Also, would the MMU in the 68030 be operable in this type of setup. 

The MMU will work, the data cache won't.

>Which leads me to another question: how difficult would it be to install a 
>68851 on the lucas board? If it's just a matter of a straight hookup like 
>the 68881, I can deal with it, if not I'd probably need a vivid description 
>of how it's done. (Do the 68851 docs give an example of this?) 

The 68851 is another story alltogether.  It sits between the 68020 and the
rest of the world (except the '881/2, which sits on the logical bus), and 
it's kind of annoying.  It changes the 68020 timing ever so slightly, and for 
the worse, so while your 68020 logic may still work, timing critical stuff 
like memory has a chance of not working any more. The '851 was designed to 
be, uh, flexible, and so there are several ways to interface it with the 
68020.  Motorola wanted to provide for logical bus cache, logical bus mastering
by something other than the 68020 without affecting the physical bus, things
like that.  So it gets a bit gnarly to do anything with it.  If you get real
serious about it, get the '851 book, and I can probably provide some pointers.
But you're much better off with the '030 for most applications.

>Which leads me to ANOTHER question: Can the 68851 be hooked up to a 68010 
>(my current processor) with ease, and if so would something like SetCpu be 
>able to detect and make use of it, despite the fact that an '020 or '030 is 
>not present in the system?

Not really.  The '851 uses the coprocessor interface and speaks in '020 signal
terms.  Only, it does its own chip selecting, rather than being externally
selected like the '881, so you'd be rather hard pressed to emulate coprocessor
cycles.  I gather the 68010 does have some kind of coprocessor space cycles,
but I don't know if they're anything the '851 would handle (I kind of went
straight from 68000 to 68020, so I don't know the 68010 that well, other than
the fact it's pretty much a 68000 from the bus protocol point of view).  Plus,
the bus conversion logic, if even possible, would give you a headache.

>...Sean.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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