Mapper

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

• Bandai 2001
• Bandai 2003
• KARNAK (Pocket Challenge V2 cartridges only)

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 memory addresses 0x40000 - 0xFFFFF. Note that only the top 768KiB of said bank can be read this way.
	$C1	RAM Bank	bbbb bbbb	RW8	Selects a 64KiB bank accessed via memory addresses 0x10000 - 0x1FFFF.
	$C2	ROM0 Bank	bbbb bbbb	RW8	Selects a 64KiB bank accessed via memory addresses 0x20000 - 0x2FFFF.
	$C3	ROM1 Bank	bbbb bbbb	RW8	Selects a 64KiB bank accessed via memory addresses 0x30000 - 0x3FFFF.

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

The "mono" WonderSwan expects that the register at $C3 will power up holding $FF.