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  Interrupt:   21h     Function:   06h
 
  Title:       Direct Console I/O
 
  See also:    Character Input, Character Output
 
  Description:
 
     Used by programs that need to read and write all possible
     characters and control codes without any interference from the
     operating system. Reads a character from the standard input device
     or writes a character to the standard output device. I/O may be
     redirected. However, if I/O has been redirected, there is no way
     to detect EOF or that the disk is full.
 
     Input                               Output
 
     AH = 06h                            If called with DL = 00h-0FEh
     DL = Function requested               None
        = 00h-FEh (if output request)
        = 0FFh (if input request)        If called with DL = FFh and a
                                         character is ready
                                           Zero flag: clear
                                           AL = 8-bit input data
 
                                         If called with DL = FFh and no
                                         character is ready
                                           Zero flag: set
                                    -♦-