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  Description:  Direct Console I/O
 
  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 (if I/O has been
  redirected, there is no way to detect EOF or disk full).
 
  Input                                    Output
  ═════════════════════════════            ═════════════════════════════
  AH=06H                                   If called with DL=00H-0FEH
  DL=function requested                    Nothing
    =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
                                    -♦-