This memory controller works much like the MBC1
  controller with the following exceptions:

  MBC2 will work with ROM sizes up to 2Mbit.

  Writing a value (XXXXBBBB - X = Don't cares, B =
  bank select bits) into 2000-3FFF area will select an
  appropriate ROM bank at 4000-7FFF.

  RAM switching is not provided. Unlike the MBC1 which
  uses external RAM, MBC2 has 512 x 4 bits of RAM which
  is in the controller itself. It still requires an
  external battery to save data during power-off though.

  The least significant bit of the upper address byte
  must be zero to enable/disable cart RAM. For example
  the following addresses can be used to enable/disable
  cart RAM:
  0000-00FF, 0200-02FF, 0400-04FF, ..., 1E00-1EFF.
  The suggested address range to use for MBC2 ram
  enable/disable is 0000-00FF.

  The least significant bit of the upper address byte
  must be one to select a ROM bank. For example the
  following addresses can be used to select a ROM bank:
  2100-21FF, 2300-23FF, 2500-25FF, ..., 3F00-3FFF.
  The suggested address range to use for MBC2 rom
  bank selection is 2100-21FF.