Path: utzoo!attcan!uunet!cs.utexas.edu!rice!uw-beaver!ubc-cs!news-server.csri.toronto.edu!qucdn!leek
From: LEEK@QUCDN.QueensU.CA
Newsgroups: comp.sys.amiga
Subject: Re: motorola/intel
Message-ID: <90263.074623LEEK@QUCDN.BITNET>
Date: 20 Sep 90 11:46:23 GMT
References: <30140@nigel.ee.udel.edu> <14427@cbmvax.commodore.com>
 <566@DIALix.UUCP>
Organization: Queen's University at Kingston
Lines: 33

In article <566@DIALix.UUCP>, bernie@DIALix.UUCP (Bernd Felsche) says:
>
>But, but what about the 680x0's MOVEP instruction?  It exists to
>support the older 6800 chips.  And presumably consumes some
>instruction decoding.

They are not restricted to 68XX perpherial chips.  The 8-bit perpherials
can also have async bus cycles.  The bus controller hardware determines
whether the devices want async or sync (68XX) cycles.  There is no software
instruction to tell it what to use.

>
>I know that "nobody" uses it, but it is there.  Or wouldn't you
>class it as an I/O instruction?  Agreed, it is not I/O mapped. but
>it *is* a special I/O instruction.

Wrong again !!  ALF2 SCSI driver uses it.  It is a special I/O instruction
only in what it does - move alternating bytes to/from a data register.  This
can speed things up as it has a lower overhead (vs 4 instructions) to transfer
4 bytes to/from a 8-bit perpherial device.   Surely it can be replaced by
MOVE.B if Motorola decided that nobody uses it and they can't live without
that Silicon real-estate.

>
>bernie
>
>| bernie@DIALix.oz.au
>| I don't sign anything until I see the money. :-)

K. C. Lee
Elec. Eng. Grad. Student

P.S.  Please read up on 68000 User's Manual by Motorola.