i386/i386.reference/LMSW.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode LMSW</TITLE>
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   7 <B>up:</B> <A HREF="c17.htm">
   8 Chapter 17 -- 80386 Instruction Set</A><BR>
   9 <B>prev:</B><A HREF="LLDT.htm"> LLDT Load Local Descriptor Table Register</A><BR>
  10 <B>next:</B><A HREF="LOCK.htm"> LOCK Assert LOCK# Signal Prefix</A>
  11 <P>
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  13 <P>
  14 <H1>LMSW -- Load Machine Status Word</H1>
  15
  16 <PRE>
  17 Opcode      Instruction      Clocks   Description
  18
  19 0F  01 /6   LMSW r/m16       10/13    Load r/m16 in machine status word
  20 </PRE>
  21
  22 <H2>Operation</H2>
  23
  24 <PRE>
  25 MSW := r/m16; (* 16 bits is stored in the machine status word *)
  26 </PRE>
  27
  28 <H2>Description</H2>
  29
  30 LMSW loads the machine status word (part of CR0) from the source
  31 operand. This instruction can be used to switch to Protected Mode; if so,
  32 it must be followed by an intrasegment jump to flush the instruction
  33 queue. LMSW will not switch back to Real Address Mode.
  34 <P>
  35 LMSW is used only in operating system software. It is not used in
  36 application programs.
  37
  38 <H2>Flags Affected</H2>
  39
  40 None
  41
  42 <H2>Protected Mode Exceptions</H2>
  43
  44 #GP(0) if the current privilege level is not 0; #GP(0) for an illegal
  45 memory operand effective address in the CS, DS, ES, FS, or GS
  46 segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
  47 for a page fault
  48
  49 <H2>Real Address Mode Exceptions</H2>
  50
  51 Interrupt 13 if any part of the operand would lie outside of the effective
  52 address space from 0 to 0FFFFH
  53
  54 <H2>Virtual 8086 Mode Exceptions</H2>
  55
  56 Same exceptions as in Real Address Mode; #PF(fault-code) for a page
  57 fault
  58
  59 <H2>Notes</H2>
  60
  61 The operand-size attribute has no effect on this instruction. This
  62 instruction is provided for compatibility with the 80286; 80386 programs
  63 should use <A HREF="MOVRS.htm">MOV</A> CR0, ... instead.
  64 <P>
  65 <HR>
  66 <P>
  67 <B>up:</B> <A HREF="c17.htm">
  68 Chapter 17 -- 80386 Instruction Set</A><BR>
  69 <B>prev:</B><A HREF="LLDT.htm"> LLDT Load Local Descriptor Table Register</A><BR>
  70 <B>next:</B><A HREF="LOCK.htm"> LOCK Assert LOCK# Signal Prefix</A>
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