Int 16h, 01h            Keyboard Status                                   all

    Checks to see if a character is available in the buffer.

        Entry   AH = 01h

        Return  ZF = 0, if character is available
                     1, if character is not available
                AL = ASCII character code (if character is available)
                AH = Scan code (if character is available)

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    If a character is available, the Zero Flag is cleared and AX
    contains the ASCII value in AL and the scan code in AH. The
    character is not removed from the buffer. Use Service 00h to
    remove the character from the buffer. See Service 00h for a
    complete description of the meaning of AX if a character is
    available.

    This service is excellent for clearing the keyboard or allowing a
    program to be interruptable by a specific key sequence.

    See Service 11h for an equivalent service that supports the
    enhanced (101/102-key) keyboard.