Mapper

There are three documented memory-mapping chips used on the WonderSwan and Pocket Challenge V2:

• Bandai 2001
• Bandai 2003
• KARNAK

All three provide this same common subset for memory banking:

Category	Port	Description	Bits	Type	Notes
Extended bankswitching	$C0	ROM Linear (EX) Bank	00BB bbbb	RW8	Selects a 1MiB bank accessed via segments 0x4000 through 0xF000.
	$C1	RAM(/ROM) Bank	bbbb bbbb	RW8	Selects a 64KiB bank accessed via segment 0x1000.
	$C2	ROM0 Bank	bbbb bbbb	RW8	Selects a 64KiB bank accessed via segment 0x2000.
	$C3	ROM1 Bank	bbbb bbbb	RW8	Selects a 64KiB bank accessed via segment 0x3000.

Note that the number of bits in the Linear bank register depends on the mapper.

The black-and-white WonderSwan expects that the register at $C3 will power up holding $FF.