51 lines
2.5 KiB
HTML
51 lines
2.5 KiB
HTML
<html><!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<html>
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<head>
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<title>80386 Programmer's Reference Manual -- Opcode LMSW</title>
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</head>
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<body>
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<b>up:</b> <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17 -- 80386 Instruction Set</a><br>
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<b>prev:</b><a href="LLDT.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LLDT.HTM"> LLDT Load Local Descriptor Table Register</a><br>
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<b>next:</b><a href="LOCK.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LOCK.HTM"> LOCK Assert LOCK# Signal Prefix</a>
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<p>
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<hr>
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<p>
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<h1>LMSW -- Load Machine Status Word</h1>
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<pre>
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Opcode Instruction Clocks Description
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0F 01 /6 LMSW r/m16 10/13 Load r/m16 in machine status word
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</pre>
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<h2>Operation</h2>
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<pre>
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MSW := r/m16; (* 16 bits is stored in the machine status word *)
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</pre>
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<h2>Description</h2>
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LMSW loads the machine status word (part of CR0) from the source operand. This instruction can be used to switch to Protected Mode; if so, it must be followed by an intrasegment jump to flush the instruction queue. LMSW will not switch back to Real Address Mode.
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<p>LMSW is used only in operating system software. It is not used in application programs.
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<h2>Flags Affected</h2>
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None
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<h2>Protected Mode Exceptions</h2>
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#GP(0) if the current privilege level is not 0; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault
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<h2>Real Address Mode Exceptions</h2>
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Interrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH
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<h2>Virtual 8086 Mode Exceptions</h2>
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Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
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<h2>Notes</h2>
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The operand-size attribute has no effect on this instruction. This instruction is provided for compatibility with the 80286; 80386 programs should use <a href="MOVRS.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/MOVRS.HTM">MOV</a> CR0, ... instead.
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<p>
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<hr>
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<p><b>up:</b> <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17 -- 80386 Instruction Set</a><br>
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<b>prev:</b><a href="LLDT.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LLDT.HTM"> LLDT Load Local Descriptor Table Register</a><br>
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<b>next:</b><a href="LOCK.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LOCK.HTM"> LOCK Assert LOCK# Signal Prefix</a>
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</body>
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