NES 2.0 Mapper 439
From NESdev Wiki
Jump to navigationJump to search
NES 2.0 Mapper 439 denotes the YS2309 UxROM-like multicart PCB. Its UNIF MAPRs are BMC-DS-07 and BMC-K86B. All registers set to $00 on reset.
Latch Register ($8000-$FFFF, write)
D~[M..PP PPPP] Address mask: $8000 | ++-++++- PRG A19..A14 when CPU A14=0, | $3F when CPU A14=1 +---------- Nametable mirroring, 0=Vertical, 1=Horizontal
This is basically an UxROM-like latch register for up to 1 MiB of PRG ROM, plus software-switchable mirroring.
Outer Bank Register ($6000, write)
D~[.PPP ....] Address mask: $E001 +++------ PRG A19..A17 if enabled via $6001
Mask Register ($6001, write)
D~[MPPP ....] Address mask: $E001 |||+------- 0: PRG A17 from Latch, 1: PRG A17 from $6000 ||+-------- 0: PRG A18 from Latch, 1: PRG A18 from $6000 |+--------- 0: PRG A19 from Latch, 1: PRG A19 from $6000 +---------- 1: Protect Mirroring bit in Latch from being changed