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From: aburto@marlin.UUCP (Alfred A. Aburto)
Newsgroups: comp.sys.amiga
Subject: Re: 68020
Message-ID: <835@marlin.UUCP>
Date: Wed, 12-Nov-86 14:47:39 EST
Article-I.D.: marlin.835
Posted: Wed Nov 12 14:47:39 1986
Date-Received: Wed, 12-Nov-86 22:01:40 EST
References: <1150@cit-vax.Caltech.Edu>
Reply-To: aburto@marlin.UUCP (Alfred A. Aburto)
Distribution: net
Organization: Naval Ocean Systems Center, San Diego
Lines: 55

In article <1150@cit-vax.Caltech.Edu> lyles@tybalt.caltech.edu.UUCP (Lyle N. Scheer) writes:
>Organization : Calfornia Institute of Technology
>Keywords: 68020, 68881
>From: lyles@tybalt.caltech.edu (Lyle N. Scheer)
>Path: tybalt.caltech.edu!lyles
>
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>A few questions.  First, is it truely possible to use a 68020 replacing the
>68000(ie, are there any problems, bugs, etc(I have a program that is said to
>make a 68010 work with the amiga, but I don't know if it will do the same thing
>with the 68020).  Second, what is the relation of the 68881 to the 68020, and,
>if you can replace the 68000 with the 68020, is there a spot for the 68881?
>
>						Wonko the Sane

Yes it is possilble to replace the Amiga's 68000 with the 68020 and
the 68881.  My Amiga is now running with a 68020/68881 in place of
the 68000.  It works very well with KickWorkbench V1.2. V1.1 does not
support the 68881 (multi-task switching problems).  The best feature
of the 68020 is its internal cache memory which helps to increase the
Amiga's performance by (roughly) a factor of two.  This is much more
of an improvement than you would get from the 68010.  Also for dramatic
improvements in floating-point processing speed the 68881 is a must.
The 68881 is designed as a co-processor for the 68020---they work
together and the 881 floating-point instructions are treated as an extension
of the 020 instruction set. That is with these co-processors an 80-bit
floating-point add (FADD.X FP0,FP1 for example) is treated as any other
020 instruction would be (such as ADD.L D0,D1).  With the 68000 or 68010
the 68881 must be treated as a peripheral---you need to trap and decode
68881 instructions and read/write to a port.

The 68000 and the 68020 are not pin-for-pin compatible. An adaptor board
is needed to replace the 68020/68881 directly with the Amiga's 68000. Or
the 68020/68881 can be interfaced to the Amiga via the expansion bus(this
has advantages because you can run the 020/881 at a higher clock speed---
CHIP memory must however still run at the standard 7.16 MHz rate).

As far as software goes there is only one compiler right now that generates
code for the 68881 with the Amiga and thats Absoft's Fortran 77 68020/68881
Amiga compiler ($495).  Also Quelo is beta testing an Amiga 68020/68881
assembler.  I have a Quelo 68020 Amiga assembler at this time. Hope soon
to get the 68881 update.

There may be others, but I'm aware of only one company that makes
68020/68881 adaptor boards and expansion boxes for the Amiga and thats
Computer System Associates , San Diego, Calif, (619) 566-3911....

If there is any interest I will upload benchmark comparison tests I've
conducted with these Amiga 68020/68881 processors and other systems.

Al Aburto