$DE02/56834/SWIFTLINK+2:   Command Register

   +----------+---------------------------------------------------+
   | Bits 7-5 |   Parity: 000 = None            101 = Mark        |
   |          |           001 = Odd             111 = Space       |
   |          |           011 = Even                              |
   | Bit  4   |   Echo: 1 = On                                    |
   | Bit  3-2 |         Transmitter IRQ |  RTS  | Transmitter     |
   |          |         ----------------+-------+------------     |
   |          |    00 =     Disabled    |  High |    Off          |
   |          |    01 =     Enabled     |  Low  |    On           |
   |          |    10 =     Disabled    |  Low  |    On           |
   |          |    11 =     Disabled    |  Low  |    BRK          |
   | Bit  1   |   Receiver Interrupt: 1 = Disabled                |
   | Bit  0   |   Master IRQ Control: 1 = On                      |
   +----------+---------------------------------------------------+