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Daniel Wilson's Notes on 80x86 Assembly

Some Useful Instructions and Interrupts

 IN and OUT -- I/O at a lower level than interrupts

INT 14H -- The Serial Communication Interrups
The following is from Assembly Language for the IBM-PC by Kip R. Irvine

IN Instruction.  The IN instruction inputs a byte or word from a port.  The syntax is
    IN accumulator, port
Port may be a constant in the range 0 -FFh, or it may be a value in DX between 0 and FFFFh.  Accumulator must be AL for 8-bit transfers, and AX for 16-bit transfers.  Examples are:

OUT Instruction.    The OUT instruction outputs a byte or word to a port.  The syntax is
    OUT port, accumulator