XCHG -- Exchange Register/Memory with Register

Opcode    Instruction      Clocks     Description

90 + r    XCHG AX,r16      3          Exchange word register with AX
90 + r    XCHG r16,AX      3          Exchange word register with AX
90 + r    XCHG EAX,r32     3          Exchange dword register with EAX
90 + r    XCHG r32,EAX     3          Exchange dword register with EAX
86  /r    XCHG r/m8,r8     3          Exchange byte register with EA byte
86  /r    XCHG r8,r/m8     3/5        Exchange byte register with EA byte
87  /r    XCHG r/m16,r16   3          Exchange word register with EA word
87  /r    XCHG r16,r/m16   3/5        Exchange word register with EA word
87  /r    XCHG r/m32,r32   3          Exchange dword register with EA dword
87  /r    XCHG r32,r/m32   3/5        Exchange dword register with EA dword

Operation

temp := DEST
DEST := SRC
SRC := temp

Description

XCHG exchanges two operands. The operands can be in either order. If a memory operand is involved, BUS LOCK is asserted for the duration of the exchange, regardless of the presence or absence of the LOCK prefix or of the value of the IOPL.

Flags Affected

None

Protected Mode Exceptions

#GP(0) if either operand is in a nonwritable segment; #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

Real Address Mode Exceptions

Interrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault

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