     $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.