Assembler:Commands:IN

command in destination, source

Input from Port. Copies the value from the I/O port specified with the second operand (source operand) to the destination operand (first operand).

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 13, Input/Output, in the IA-32 Intel Architecture Software Developer's Manual, Volume 1, for more information on accessing I/O ports in the I/O address space. 64-ia-32-architectures-software-developer-vol-1-manual.pdf

c9x.me/x86/html/file_module_x86_id_139.html

Command Parameters

Parameter	Description
destination	The destination of the byte(s) read
source	The I/O port number to read

See also

• Assembler
• Auto Assembler
• Assembler Commands

External links

• wikipedia.org/wiki/X86_instruction_listings
• wikibooks.org/wiki/X86_Assembly/Other_Instructions
• c9x.me/x86/
• ref.x86asm.net
• https://www.felixcloutier.com/x86