Nintendo DMG-01 - Game Boy Console Manual page 14

2.6. Cartridge Types
Rom bank 0 is not accessible from 4000-7FFF and can
only be read from 0000-3FFF.
If memory model is set to 4/32:
Writing a value (XXXXXXBB - X = Don't care, B =
bank select bits) into 4000-5FFF area will select
an appropriate RAM bank at A000-C000. Before you
can read or write to a RAM bank you have to enable
it by writing a XXXX1010 into 0000-1FFF area*. To
disable RAM bank operations write any value but
XXXX1010 into 0000-1FFF area. Disabling a RAM bank
probably protects that bank from false writes
during power down of the GameBoy. (NOTE: Nintendo
suggests values $0A to enable and $00 to disable
RAM bank!!)
If memory model is set to 16/8 mode:
Writing a value (XXXXXXBB - X = Don't care, B =
bank select bits) into 4000-5FFF area will set the
two most significant ROM address lines.
* NOTE: The Super Smart Card doesn't require this
operation because it's RAM bank is ALWAYS enabled.
Include this operation anyway to allow your code
to work with both.
MBC2 (Memory Bank Controller 2):
•
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
Page 14
TM
Game Boy CPU Manual
V 1.01