hw/i386.reference/MOVS.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode MOVS</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="MOVRS.htm"> MOV Move to/from Special Registers</A><BR>
  10 <B>next:</B><A HREF="MOVSX.htm"> MOVSX Move with Sign-Extend</A>
  11 <P>
  12 <HR>
  13 <P>
  14 <H1>MOVS/MOVSB/MOVSW/MOVSD -- Move Data from String to String</H1>
  15
  16 <PRE>
  17 Opcode  Instruction      Clocks   Description
  18
  19 A4      MOVS m8,m8       7        Move byte [(E)SI] to ES:[(E)DI]
  20 A5      MOVS m16,m16     7        Move word [(E)SI] to ES:[(E)DI]
  21 A5      MOVS m32,m32     7        Move dword [(E)SI] to ES:[(E)DI]
  22 A4      MOVSB            7        Move byte DS:[(E)SI] to ES:[(E)DI]
  23 A5      MOVSW            7        Move word DS:[(E)SI] to ES:[(E)DI]
  24 A5      MOVSD            7        Move dword DS:[(E)SI] to ES:[(E)DI]
  25 </PRE>
  26
  27 <H2>Operation</H2>
  28
  29 <PRE>
  30 IF (instruction = MOVSD) OR (instruction has doubleword operands)
  31 THEN OperandSize := 32;
  32 ELSE OperandSize := 16;
  33 IF AddressSize = 16
  34 THEN use SI for source-index and DI for destination-index;
  35 ELSE (* AddressSize = 32 *)
  36    use ESI for source-index and EDI for destination-index;
  37 FI;
  38 IF byte type of instruction
  39 THEN
  40    [destination-index] := [source-index]; (* byte assignment *)
  41    IF DF = 0 THEN IncDec := 1 ELSE IncDec := -1; FI;
  42 ELSE
  43    IF OperandSize = 16
  44    THEN
  45       [destination-index] := [source-index]; (* word assignment *)
  46       IF DF = 0 THEN IncDec := 2 ELSE IncDec := -2; FI;
  47    ELSE (* OperandSize = 32 *)
  48       [destination-index] := [source-index]; (* doubleword assignment *)
  49       IF DF = 0 THEN IncDec := 4 ELSE IncDec := -4; FI;
  50    FI;
  51 FI;
  52 source-index := source-index + IncDec;
  53 destination-index := destination-index + IncDec;
  54 </PRE>
  55
  56 <H2>Description</H2>
  57
  58 MOVS copies the byte or word at [(E)SI] to the byte or word at
  59 ES:[(E)DI]. The destination operand must be addressable from the ES
  60 register; no segment override is possible for the destination. A segment
  61 override can be used for the source operand; the default is DS.
  62 <P>
  63 The addresses of the source and destination are determined solely by the
  64 contents of (E)SI and (E)DI. Load the correct index values into (E)SI
  65 and (E)DI before executing the MOVS instruction. MOVSB, MOVSW,
  66 and MOVSD are synonyms for the byte, word, and doubleword MOVS
  67 instructions.
  68 <P>
  69 After the data is moved, both (E)SI and (E)DI are advanced
  70 automatically. If the direction flag is 0 (<A HREF="CLD.htm">CLD</A> was executed), the registers
  71 are incremented; if the direction flag is 1 (<A HREF="STD.htm">STD</A> was executed), the
  72 registers are decremented. The registers are incremented or decremented by 1
  73 if a byte was moved, 2 if a word was moved, or 4 if a doubleword was moved.
  74 <P>
  75 MOVS can be preceded by the
  76 <A HREF="REP.htm">REP</A> prefix for block movement of CX
  77 bytes or words. Refer to the
  78 <A HREF="REP.htm">REP</A> instruction for details of this operation.
  79
  80 <H2>Flags Affected</H2>
  81
  82 None
  83
  84 <H2>Protected Mode Exceptions</H2>
  85
  86 #GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
  87 memory operand effective address in the CS, DS, ES, FS, or GS
  88 segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
  89 for a page fault
  90
  91 <H2>Real Address Mode Exceptions</H2>
  92
  93 Interrupt 13 if any part of the operand would lie outside of the effective
  94 address space from 0 to 0FFFFH
  95
  96 <H2>Virtual 8086 Mode Exceptions</H2>
  97
  98 Same exceptions as in Real Address Mode; #PF(fault-code) for a page
  99 fault
 100 <P>
 101 <HR>
 102 <P>
 103 <B>up:</B> <A HREF="c17.htm">
 104 Chapter 17 -- 80386 Instruction Set</A><BR>
 105 <B>prev:</B><A HREF="MOVRS.htm"> MOV Move to/from Special Registers</A><BR>
 106 <B>next:</B><A HREF="MOVSX.htm"> MOVSX Move with Sign-Extend</A>
 107 </BODY>