Path: utzoo!attcan!uunet!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.m68k
Subject: Re: opcode emulation (Was: Re: 68020 in a *68010* socket?)
Message-ID: <4015@cbmvax.UUCP>
Date: 13 Jun 88 22:09:12 GMT
References: <3447@pdn.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 28

in article <3447@pdn.UUCP>, alan@pdn.UUCP (Alan Lovejoy) says:
> 
> Howerver, there is the mc68012, which if I remember correctly is
> completely software compatible with the 68020 but pin-compatible with
> the 68010.  But my memory is rather vague on this part.  Perhaps someone
> else has more authoritative info?

The fact that the 68012 and 68010 are in the same Technical Note was my
first clue.  The 68012 is basically a 68010 in a larger package.  It
brings out a few more pins, like an extra address line or two, and I
think the '020 style RMC pin, but it doesn't do any 68020 style op-codes.

The other thing to consider with all this backward compatibility talk would
be how much '020 software do you really have available.  If there's lots,
maybe a '020 in a 68000 compatible package of some kind would be nice, and
it would also be a nice way to support math in a 68000 based system.  The
68020 at the same speed would run slower than the 68000 on a 16 bit bus,
though, for many operations.  All that 32 bit prefetching.  So if you're
running 68000 code with no floating point, a plain 68020 drop in will 
often hurt your performance and give you little in return (ok, it does
get something back on tight loops if your OS lets you run with the cache
on).

> Alan Lovejoy; alan@pdn; 813-530-8241; Paradyne Corporation: Largo, Florida.
-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {ihnp4|uunet|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
		"I can't relax, 'cause I'm a Boinger!"