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From: leed@hplsla.UUCP
Newsgroups: comp.sys.m68k
Subject: Re: Question about 68K registers
Message-ID: <590001@hplsla.HP.COM>
Date: Thu, 26-Mar-87 18:09:04 EST
Article-I.D.: hplsla.590001
Posted: Thu Mar 26 18:09:04 1987
Date-Received: Sun, 29-Mar-87 12:01:19 EST
References: <1055@tekred.TEK.COM>
Organization: HP Lake Stevens
Lines: 18



	On the address  register  issue, I don't have an  opinion.  

	On the data register, I do.  The reason you don't want byte or
	word  operations to affect the upper bits is because the upper
	bits could be holding data that you do not want to be affected
	by operations on the lower 8/16 bits.  This can be useful when
	most of your  data is in a 16 bit  format  and you  need  more
	registers.  You can  access  the  upper  bits  using  the SWAP
	instruction.

	That is my guess.

	Lee Darrow
	Hewlett Packard
	hplsla!leed
	(206)-335-2619