Article View: comp.sys.intel
Article #902Re: Undocumented instructions in x86 CPUs
From: Morten Welinder
Date: Sat, 07 Nov 1992 15:45
Date: Sat, 07 Nov 1992 15:45
33 lines
1674 bytes
1674 bytes
mostert@cs.sun.ac.za (A. Mostert) writes:
>In article <1992Nov5.101717.26632@umr.edu> mcastle@mcs213d.cs.umr.edu (Michael R Castle) writes:
>>In article <mostert.51@cs.sun.ac.za> mostert@cs.sun.ac.za (A. Mostert) writes:
>>>I just became aware of an undocumented instruction that (I think) works on
>>>all members of the x86 family. The opcode is D4 10 and it does this:
> ^^^^
>>> AH = AL >> 4
>>> AL = AL & 0xF
>>hmm.... listed in my Microprocessors and Peripheral Handbook... AAM
>AAM is opcode D4 0A
>AAD is opcode D5 0A
>The second byte is actually a number specifying the base, as various people
>pointed out to me since my original posting. However, only the form with 0A
>as base is officialy documented by Intel.
>Can anyone tell me if this works on the NEC v20/V30 processors ?
>A. Mostert
>mostert@cs.sun.ac.za
From memory: AAM does, AAD does not.
Morten Welinder
terra@diku.dk
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Path: arc1-ca.pugleaf.net!sparky!uunet!mcsun!sunic!dkuug!dkuug!diku!terra From: terra@diku.dk (Morten Welinder) Newsgroups: comp.sys.intel Subject: Re: Undocumented instructions in x86 CPUs Message-ID: <1992Nov7.154508.11802@odin.diku.dk> Date: 7 Nov 92 15:45:08 GMT References: <mostert.51@cs.sun.ac.za> <1992Nov5.101717.26632@umr.edu> <mostert.54@cs.sun.ac.za> Sender: terra@rimfaxe.diku.dk Organization: Department of Computer Science, U of Copenhagen Lines: 33