     $DF01/57089/REU+1:   Command Register

       +----------+---------------------------------------------------+
       | Bit  7   |   Execute: 1 = Transfer current Configuration     |
       |          |   (not used with RAMLink)                         |
       | Bit  6   |   Reserved (normally 0)                           |
       | Bit  5   |   Load: 1 = enable autoload option (addresses and |
       |          |             transfer-length are restored to       |
       |          |             values at beginning of transfer)      |
       |          |         0 = addresses stay at last_byte_used+1    |
       |          |             and transfer-length is $0001          |
       | Bit  4   |   FF00: 1 = start immediately                     |
       |          |         0 = wait for write access to $FF00        |
       |          |   (not used with RAMLink)                         |
       | Bits 3-2 |   Reserved (normally 0)                           |
       | Bits 1-0 |   Transfer Type:  00 = transfer C64 -> REU        |
       |          |                   01 = transfer REU -> C64        |
       |          |                   10 = swap C64 <-> REU           |
       |          |                   11 = compare C64 - REU          |
       +----------+---------------------------------------------------+