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OUT -- Output to Port

Opcode    Instruction     Clocks          Description

E6  ib    OUT imm8,AL     10,pm=4*/24**   Output byte AL to immediate port
                                          number
E7  ib    OUT imm8,AX     10,pm=4*/24**   Output word AL to immediate port
                                          number
E7  ib    OUT imm8,EAX    10,pm=4*/24**   Output dword AL to immediate
                                          port number
EE        OUT DX,AL       11,pm=5*/25**   Output byte AL to port number in
DX
EF        OUT DX,AX       11,pm=5*/25**   Output word AL to port number in
DX
EF        OUT DX,EAX      11,pm=5*/25**   Output dword AL to port number
                                          in DX

Notes

*If CPL <= IOPL **If CPL > IOPL or if in virtual 8086 mode

Operation

IF (PE = 1) AND ((VM = 1) OR (CPL > IOPL))
THEN (* Virtual 8086 mode, or protected mode with CPL > IOPL *)
   IF NOT I-O-Permission (DEST, width(DEST))
   THEN #GP(0);
   FI;
FI;
[DEST] := SRC; (* I/O address space used *)

Description

OUT transfers a data byte or data word from the register (AL, AX, or EAX) given as the second operand to the output port numbered by the first operand. Output to any port from 0 to 65535 is performed by placing the port number in the DX register and then using an OUT instruction with DX as the first operand. If the instruction contains an eight-bit port ID, that value is zero-extended to 16 bits.

Flags Affected

None

Protected Mode Exceptions

#GP(0) if the current privilege level is higher (has less privilege) than IOPL and any of the corresponding I/O permission bits in TSS equals 1

Real Address Mode Exceptions

None

Virtual 8086 Mode Exceptions

#GP(0) fault if any of the corresponding I/O permission bits in TSS equals 1

up: Chapter 17 -- 80386 Instruction Set
prev: OR Logical Inclusive OR
next: OUTS/OUTSB/OUTSW/OUTSD Output String to Port