     $DE00-$DEFF/56832-57087:   AR-I/O-Register (mirrored)

       +-------+--------------------------------------------------------+
       | Bit 7 |   extra ROM bank selector (A15) (unused)               |
       | Bit 6 |   1 = resets FREEZE-mode (turns back to normal mode)   |
       | Bit 5 |   1 = enable RAM at ROML ($8000-$9FFF) &               |
       |       |       I/O2 ($DF00-$DFFF = $9F00-$9FFF)                 |
       | Bit 4 |   ROM bank selector high (A14)                         |
       | Bit 3 |   ROM bank selector low  (A13)                         |
       | Bit 2 |   1 = disable cartridge (turn off $DE00)               |
       | Bit 1 |   1 = /EXROM high                                      |
       | Bit 0 |   1 = /GAME low                                        |
       +-------+--------------------------------------------------------+

       Careful: Even a read-access will cause data to be written here!