image/svg+xmlIN—Input from PortInstruction Operand EncodingDescriptionCopies 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 infor-mation 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.OperationIF ((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 AffectedNoneOpcodeInstructionOp/ En64-Bit ModeCompat/Leg ModeDescriptionE4 ibIN AL, imm8IValidValidInput byte from imm8 I/O port address into AL.E5 ibIN AX, imm8IValidValidInput word from imm8 I/O port address into AX.E5 ibIN EAX, imm8IValidValidInput dword from imm8 I/O port address into EAX.ECIN AL,DXZOValidValidInput byte from I/O port in DX into AL.EDIN AX,DXZOValidValidInput word from I/O port in DX into AX.EDIN EAX,DXZOValidValidInput doubleword from I/O port in DX into EAX.Op/EnOperand 1Operand 2Operand 3Operand 4Iimm8NANANAZONANANANA

image/svg+xmlProtected 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 ExceptionsSame 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.

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