Newsgroups: comp.sys.amiga.programmer
Path: utzoo!utgpu!watserv1!watdragon!rose.waterloo.edu!ccplumb
From: ccplumb@rose.waterloo.edu (Colin Plumb)
Subject: Re: Instructions on 68000
Message-ID: <1991Apr12.071502.15493@watdragon.waterloo.edu>
Sender: news@watdragon.waterloo.edu (News Owner)
Organization: University of Waterloo
References: <4577@orbit.cts.com>
Date: Fri, 12 Apr 1991 07:15:02 GMT
Lines: 26

koleman@pnet51.orb.mn.org (Kurt "Koleman" Koller) wrote:
>  Ok, I was looking at some source in Assembly, and I saw some instructions
> that I wasn't familiar with.  My assembler (Macro 68) assembles them just
> fine, and they ARE mentioned in the 68000 manual, but just MENTIONED.  I
> have no idea what they do.  If anyone can help me, so be it.
 
>                st       (MemoryLocation)
>                sne      d(n)
>                sf
>                sge

>  These are not "documented" instructions.  What do they do, and why would
> someone use them other than to save cycles or 10?  Are they also used on the
> 020 030 040 etc?

These are the "set conditional" instructions, which are documented under
"Scc" like all the branches are collectively called "Bcc".
If the condition is true ("t" is always true, "f" never is), they
set the destination byte to all 1's, otherwise they clear it to
all 0's.

Obviously, their function can be emulated with other instruction
sequences (conditional branches are easiest), but that's true of
most 68000 instructions.
-- 
	-Colin
