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Q61054: Erroneous 8086 Opcode for Logical AND Instruction

Article: Q61054
Product(s): See article
Version(s): m5.10 5.10a | 5.10 5.10a
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | buglist5.10 | mspl13_masm
Last Modified: 12-JUN-1990

Problem:

I bought an operating system for a V25 processor that runs with the
INTEL 8086 instruction set. The operating system source code was
assembled with MASM 5.10 and the .8086 directive. The instruction runs
on an 8086 machine, but the machine with the V25 processor hangs at
the following instruction:

      AND Word Ptr [S+10], -5 ; Opcode generated is
                              ; 83 64 0A FB

Response:

In Appendix A-4 of the INTEL 8086/8088 programmer's reference manual
(1986 edition), there is no opcode for AND that begins with 83. There
is an opcode for AND that begins with 81. The opcode for AND reads as
follows:

   81 64 0A 00 FB

However, there is an opcode for a sign-extended immediate instruction
in the 80386 instruction set that has the first byte of the opcode as
83.

The V25 adheres strictly to INTEL's 8086 standard and will not accept
an 80386 instruction rather than an 8086 instruction.

Microsoft has confirmed this to be a problem in MASM Version 5.10. We
are researching this problem and will post new information here as it
becomes available.

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