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From: coburn@clo.dec.com (John T. Coburn)
Newsgroups: comp.sys.dec
Subject: Re: PDP-11 movb instruction
Message-ID: <377@mountn.dec.com>
Date: 29 Jun 89 01:59:52 GMT
Sender: news@mountn.dec.com
Organization: Digital Equipment Corporation
Lines: 16

In article <2592@blake.acs.washington.edu>, erf@blake.acs.washington.edu (John Firestone) writes...
>I am designing a Q-bus controller and have come upon a PDP-11
>architecture question which I hope someone can answer.  If
>a MOVB instruction writes the low byte of a word-oriented device
>register, what does the high byte get set to?
> 
>Thanks in advance for your help.
> 

The high byte would be unchanged if the device register allows byte access. 
Otherwise the result would be undefined.

--
John

Employed by, but not representing Digital Equipment Corp.