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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode MOVS</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="MOVRS.htm"> MOV Move to/from Special Registers</A><BR><B>next:</B><A HREF="MOVSX.htm"> MOVSX Move with Sign-Extend</A><P><HR><P><H1>MOVS/MOVSB/MOVSW/MOVSD -- Move Data from String to String</H1><PRE>Opcode Instruction Clocks DescriptionA4 MOVS m8,m8 7 Move byte [(E)SI] to ES:[(E)DI]A5 MOVS m16,m16 7 Move word [(E)SI] to ES:[(E)DI]A5 MOVS m32,m32 7 Move dword [(E)SI] to ES:[(E)DI]A4 MOVSB 7 Move byte DS:[(E)SI] to ES:[(E)DI]A5 MOVSW 7 Move word DS:[(E)SI] to ES:[(E)DI]A5 MOVSD 7 Move dword DS:[(E)SI] to ES:[(E)DI]</PRE><H2>Operation</H2><PRE>IF (instruction = MOVSD) OR (instruction has doubleword operands)THEN OperandSize := 32;ELSE OperandSize := 16;IF AddressSize = 16THEN use SI for source-index and DI for destination-index;ELSE (* AddressSize = 32 *) use ESI for source-index and EDI for destination-index;FI;IF byte type of instructionTHEN [destination-index] := [source-index]; (* byte assignment *) IF DF = 0 THEN IncDec := 1 ELSE IncDec := -1; FI;ELSE IF OperandSize = 16 THEN [destination-index] := [source-index]; (* word assignment *) IF DF = 0 THEN IncDec := 2 ELSE IncDec := -2; FI; ELSE (* OperandSize = 32 *) [destination-index] := [source-index]; (* doubleword assignment *) IF DF = 0 THEN IncDec := 4 ELSE IncDec := -4; FI; FI;FI;source-index := source-index + IncDec;destination-index := destination-index + IncDec;</PRE><H2>Description</H2>MOVS copies the byte or word at [(E)SI] to the byte or word atES:[(E)DI]. The destination operand must be addressable from the ESregister; no segment override is possible for the destination. A segmentoverride can be used for the source operand; the default is DS.<P>The addresses of the source and destination are determined solely by thecontents of (E)SI and (E)DI. Load the correct index values into (E)SIand (E)DI before executing the MOVS instruction. MOVSB, MOVSW,and MOVSD are synonyms for the byte, word, and doubleword MOVSinstructions.<P>After the data is moved, both (E)SI and (E)DI are advancedautomatically. If the direction flag is 0 (<A HREF="CLD.htm">CLD</A> was executed), the registersare incremented; if the direction flag is 1 (<A HREF="STD.htm">STD</A> was executed), theregisters are decremented. The registers are incremented or decremented by 1if a byte was moved, 2 if a word was moved, or 4 if a doubleword was moved.<P>MOVS can be preceded by the <A HREF="REP.htm">REP</A> prefix for block movement of CXbytes or words. Refer to the <A HREF="REP.htm">REP</A> instruction for details of this operation.<H2>Flags Affected</H2>None<H2>Protected Mode Exceptions</H2>#GP(0) if the result is in a nonwritable segment; #GP(0) for an illegalmemory operand effective address in the CS, DS, ES, FS, or GSsegments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)for a page fault<H2>Real Address Mode Exceptions</H2>Interrupt 13 if any part of the operand would lie outside of the effectiveaddress space from 0 to 0FFFFH<H2>Virtual 8086 Mode Exceptions</H2>Same exceptions as in Real Address Mode; #PF(fault-code) for a pagefault<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="MOVRS.htm"> MOV Move to/from Special Registers</A><BR> <B>next:</B><A HREF="MOVSX.htm"> MOVSX Move with Sign-Extend</A></BODY>⌨️ 快捷键说明
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