Article View: comp.sys.dec
Article #470Re: PDP-11 movb instruction
From: Bruce Wright
Date: Fri, 30 Jun 1989 02:15
Date: Fri, 30 Jun 1989 02:15
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In article <377@mountn.dec.com>, coburn@clo.dec.com (John T. Coburn) writes: > In article <2592@blake.acs.washington.edu>, erf@blake.acs.washington.edu (John Firestone) writes... > >If a MOVB instruction writes the low byte of a word-oriented device > >register, what does the high byte get set to? > > The high byte would be unchanged if the device register allows byte access. > Otherwise the result would be undefined. I think officially this is true - but in practice, essentially all implementations of the PDP-11 architecture will sign extend the byte to either all 0's or all 1's depending on the setting of bit 7. Bruce C. WrighT
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Path: arc1-ca.pugleaf.net!utzoo!attcan!uunet!husc6!rutgers!mcnc!rti!bcw From: bcw@rti.UUCP (Bruce Wright) Newsgroups: comp.sys.dec Subject: Re: PDP-11 movb instruction Summary: movb to PDP-11 device space Message-ID: <3054@rti.UUCP> Date: 30 Jun 89 02:15:38 GMT References: <377@mountn.dec.com> Organization: Research Triangle Institute, RTP, NC Lines: 13