Re: Undocumented instructions in x86 CPUs

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Article #901

#901

From: A. Mostert
Date: Sat, 07 Nov 1992 11:24

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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

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Path: arc1-ca.pugleaf.net!sparky!uunet!psgrain!ee.und.ac.za!hippo!rga1.itrga.sun.ac.za!mostert
From: mostert@cs.sun.ac.za (A. Mostert)
Subject: Re: Undocumented instructions in x86 CPUs
Message-ID: <mostert.54@cs.sun.ac.za>
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Date: Sat, 7 Nov 1992 11:24:10 GMT
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