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80386 Programmer's Reference Manual -- Opcode OUT

OUT -- Output to Port

Opcode	Instruction	Clocks	Description	Example
E6 ib	outb al,imm8	10,pm=4/24*	Output byte AL to immediate port number	`outb %al,$0x7f`
E7 ib	outw ax,imm8	10,pm=4/24*	Output word AL to immediate port number	`outw %ax,$0x7f`
E7 ib	outl eax,imm8	10,pm=4/24*	Output dword AL to immediate port number	`outl %eax,$0x7f`
EE	outb al,dx	11,pm=5/25*	Output byte AL to port number in	`outb %al,%dx`
EF	outw ax,dx	11,pm=5/25*	Output word AL to port number in	`outw %ax,%dx`
EF	outl eax,dx	11,pm=5/25*	Output dword AL to port number in DX	`outl %eax,%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

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