IN - Input Byte or Word From Port

        Usage:  IN      accum,port
        Modifies flags: None

        A byte, word or dword is read from port and placed in AL, AX or
        EAX respectively.  If the port number is in the range of 0-255
        it can be specified as an immediate, otherwise the port number
        must be specified in DX.  Valid port ranges on the PC are 0-1024,
        though values through 65535 may be specified and recognized by
        third party vendors and PS/2's.

                                 Clocks                 Size
        Operands         808x  286   386    486         Bytes

        accum,immed8    10/14   5     12     14           2
        accum,immed8 (PM)            6/26  8/28/27        2
        accum,DX         8/12   5     13     14           1
        accum,DX (PM)                7/27  8/28/27        1

        - 386+ protected mode timings depend on privilege levels.

          first number is the timing if:    CPL  IOPL
          second number is the timing if:   CPL > IOPL or in VM 86 mode (386)
                                            CPL  IOPL  (486)
          third number is the timing when:    virtual mode on 486 processor
        - 486 virtual mode always requires 27 cycles

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