+------------------------------------------------------------------------
  |
  |      MMC64-Cartridge:
  |
  +------------------------------------------------------------------------
  |
  | Used I/O-Area:
  |
  |   $DF10/57104/MMC+0        SPI Transfer Register
  |   $DF11/57105/MMC+1        Control Register
  |   $DF12/57106/MMC+2        Status Register (read only)
  |   $DF13/57107/MMC+3        Identification Register
  |
  | If Clock Port is used (Location depends on Bit 3 of $DF11):
  |
  |   $DF21/57121              Clock Port En-/Disable
  |   $DF22-$DF2F/57122-57135  Clock Port I/O-Area
  |    (or $DE01/56833 and $DE02-$DE0F/56384-56847)
  |
  | Memory Map:
  |
  |   $8000-$9FFF/32768-40959  MMC64-BIOS ROM
  |     ROM is active when Bit 0 of $DF11 and the Flash jumper is not set
  |     ROM is write enabled when Bit 4 of $DF11 and Flash jumper is set
  |
  +------------------------------------------------------------------------