$DE09/56841/RR+9:   SilverSurfer: Interrupt Enable Register
                                   Baud Rate Divisor MSB

  Receive/Transmit Buffer     (if Bit 7 of $DE0B is 0)

   +-------+--------------------------------------------------------+
   | Bit 3 |   1 = enable Modem Status change-Interrupt             |
   | Bit 2 |   1 = enable Reciever Line Status-Interrupt            |
   | Bit 1 |   1 = enable Transmit Holding Register empty (THRE)    |
   | Bit 0 |   1 = enable Data available-Interrupt (and Timeout) (*)|
   +-------+--------------------------------------------------------+

   (*) 16550 will interrupt if data exists in the FIFO and isn't read
       within the time it takes to receive four bytes or if no data
       is received within the time it takes to receive four bytes.

  Baud Rate Divisor High Byte (if Bit 7 of $DE0B is 1)

   See $DE08 for details.