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INT 16h,  01h (1)        Keyboard Status                                  all

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

       On entry:      AH         01h

       Returns:       Zero       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)

  --------------------------------------------------------------------------

       Notes:         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.