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  Description:  Read Character from Communications Port      [PC] [AT] [PS/2]
 
  Reads a character from the specified serial communications port, also
  returning the port's status.
 
  Input                             Output
  ═════════════════════════════     ═════════════════════════════════════════
  AH=02H                            If function successful
  DX=communications port number     AH bit 7=0
     (0=COM1, 1=COM2,   etc.)       AH bits 0-6=status
                                                Bit(s)  Significance (if set)
                                                ══════  ═════════════════════
                                                4       break detected
                                                3       framing error detected
                                                2       parity error detected
                                                1       overrun error detected
                                    AL=character
                                    If function unsuccessful (timed-out)
                                    AH bit 7=1
                                    -♦-