IN

This instruction reads a byte from I/O memory and stores it in the destination operand. The flags are not affected.

Usage

IN dest, source

source refers to the I/O port or memory address. It can be an 8-bit immediate value (see operand types) or the DX register. If DX is used, the word stored in the register will be used as the I/O memory address.

dest can be AL or AX. If it is AX, the byte will first be read from the port specified by source and stored in AL, and then read from the next port and stored in AH.

Encoding

• Fixed port
  0101000w, port
• Variable port
  0101001w

Where w is the output size bit. w=0 indicates storing the output in AL and w=1 in AX.