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From: conan@ccwf.cc.utexas.edu (Robert Faulkner)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Instructions on 68000
Summary: Scc Instuction and its use !!
Keywords: Scc 68000 Assembly
Message-ID: <47118@ut-emx.uucp>
Date: 12 Apr 91 21:43:49 GMT
References: <4577@orbit.cts.com>
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Reply-To: conan@ccwf.cc.utexas.edu (Robert Faulkner)
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In-reply-to: koleman@pnet51.orb.mn.org (Kurt "Koleman" Koller)
Originator: conan@dopey.cc.utexas.edu

>From: koleman@pnet51.orb.mn.org (Kurt "Koleman" Koller)
>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
 
>etc...
> 
> 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 Set According to Condition commands in the form Scc <ea>
The specified condition code is Tested, if the condition is true, the
byte specified by the effective address is set to TRUE, (all ones),
otherwise that byte is set to False (all zeroes), "CC" may specify the
following conditions

CC	Carry Clear		LS 	Low or Same
CS	Carry Set		LT	Less Than
EQ	Equal			MI	Minus
F	False 			NE	Not Equal
GE	Greater or Equal	PI	Plus
GT	Greater Than		T	True
HI	High			VC	Overflow Clear
LE	Less or Equal		VS	OverFlow Set

This command is a good way to set a Boolean Flag byte in a return value
for a function.  As far as I know it is supported on all of the 680x0
processors.  Feel free to e-mail me with any other questions.

I got all of this information from the S68000 User's Guide, which only
costs about $0.65 at our University Book Store.  You can also call 
Signetics and they will send you one free, plus a bunch of other useful
information on the 68000.

The phone # is 408-739-7700, ask for publications department.

Thanks,

-- 

Robert Faulkner                              conan@ccwf.cc.utexas.edu
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