# IN — Input From Port

Opcode | Instruction | Op/En | 64-Bit Mode | Compat/Leg Mode | Description
--- | --- | --- | --- | --- | ---
E4 ib | IN AL, imm8 | I | Valid | Valid | Input byte from imm8 I/O port address into AL.
E5 ib | IN AX, imm8 | I | Valid | Valid | Input word from imm8 I/O port address into AX.
E5 ib | IN EAX, imm8 | I | Valid | Valid | Input dword from imm8 I/O port address into EAX.
EC | IN AL,DX | ZO | Valid | Valid | Input byte from I/O port in DX into AL.
ED | IN AX,DX | ZO | Valid | Valid | Input word from I/O port in DX into AX.
ED | IN EAX,DX | ZO | Valid | Valid | Input doubleword from I/O port in DX into EAX.

## Instruction Operand Encoding ¶

Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4
--- | --- | --- | --- | ---
I | imm8 | N/A | N/A | N/A
ZO | N/A | N/A | N/A | N/A

## Description ¶

Copies the value from the I/O port specified with the second operand (source operand) to the destination operand (first operand). The source operand can be a byte-immediate or the DX register; the destination operand can be register AL, AX, or EAX, depending on the size of the port being accessed (8, 16, or 32 bits, respectively). Using the DX register as a source operand allows I/O port addresses from 0 to 65,535 to be accessed; using a byte immediate allows I/O port addresses 0 to 255 to be accessed.

When accessing an 8-bit I/O port, the opcode determines the port size; when accessing a 16- and 32-bit I/O port, the operand-size attribute determines the port size. At the machine code level, I/O instructions are shorter when accessing 8-bit I/O ports. Here, the upper eight bits of the port address will be 0.

This instruction is only useful for accessing I/O ports located in the processor’s I/O address space. See Chapter 19, “Input/Output,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for more information on accessing I/O ports in the I/O address space.

This instruction’s operation is the same in non-64-bit modes and 64-bit mode.

## Operation ¶

    IF ((PE = 1) and ((CPL > IOPL) or (VM = 1)))
        THEN (* Protected mode with CPL > IOPL or virtual-8086 mode *)
            IF (Any I/O Permission Bit for I/O port being accessed = 1)
                THEN (* I/O operation is not allowed *)
                    #GP(0);
                ELSE ( * I/O operation is allowed *)
                    DEST := SRC; (* Read from selected I/O port *)
            FI;
        ELSE (Real Mode or Protected Mode with CPL ≤ IOPL *)
            DEST := SRC; (* Read from selected I/O port *)
    FI;

## Flags Affected ¶

None.

## Protected Mode Exceptions ¶

#GP(0) | If the CPL is greater than (has less privilege) the I/O privilege level (IOPL) and any of the corresponding I/O permission bits in TSS for the I/O port being accessed is 1.
#PF(fault-code) | If a page fault occurs.
#UD | If the LOCK prefix is used.

## Real-Address Mode Exceptions ¶

#UD | If the LOCK prefix is used.

## Virtual-8086 Mode Exceptions ¶

#GP(0) | If any of the I/O permission bits in the TSS for the I/O port being accessed is 1.
#PF(fault-code) | If a page fault occurs.
#UD | If the LOCK prefix is used.

## Compatibility Mode Exceptions ¶

Same exceptions as in protected mode.

## 64-Bit Mode Exceptions ¶

#GP(0) | If the CPL is greater than (has less privilege) the I/O privilege level (IOPL) and any of the corresponding I/O permission bits in TSS for the I/O port being accessed is 1.
#PF(fault-code) | If a page fault occurs.
#UD | If the LOCK prefix is used.