Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!gem.mps.ohio-state.edu!sunybcs!rutgers!bpa!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Commodore New Products/Price Reductions COMDEX Announcements
Message-ID: <8754@cbmvax.UUCP>
Date: 29 Nov 89 16:30:26 GMT
References: <21450@usc.edu>
Organization: Commodore Technology, West Chester, PA
Lines: 37

in article <21450@usc.edu>, papa@pollux.usc.edu (Marco Papa) says:

> In article <787@crash.cts.com> lgreen@pnet01.cts.com (Lawrence Greenwald) writes:
> |papa@pollux.usc.edu (Marco Papa) writes:
> ||Last week at COMDEX Commodore announced new products and price reductions.
> ||The following excerpts are taken from the press releases:
> ||* Commodore Amiga 2630

> ||A Motorola 68030-based accelerator, 25MHz MC68030,
> ||25MHz MC68882 math co-processor, 68851 MMU, 2MB of
				^^^^^^^^^^^^^^^^^^^
> |Hey Marco, is this one verbatim from a Commodore handout? 

> Yep. that's what BOTH press releases on the A2630 and A2500/30 state. 

Someone's obviously confused; of course there's no 68851 MMU on the
A2630.  The 68030 doesn't even generate the coprocessor address for the
MMU, so even if you hooked one up, it wouldn't do anything more than
eat up a few watts of power and get in the way.

While it's not common knowledge, the 68851 is EVIL.  It sits there and 
does it's MMUing, which is fine though a bit weird to hook up (if you 
though the normal 3-wire bus arbitration practiced by most Motorola
things was weird, take a look at the 5-wire bus arbitration this MMU
uses).  But not only does it add a wait state, it extends things just a
bit more, so now signals that used to be well behaved, changing within
a given clock pulse, become wicked and can hang over clock edges.  So
if you really want your system to work, the 68851 can end up adding
even more delay.  And complexity.  Which is why A2620s go at 14.3MHz
and A2630s go at 25MHz...

> -- Marco Papa 'Doc'

-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough