NES 2.0 Mapper 521 is used for 장두진 바둑교실: 입문편, commonly known as Korean Igo. Its UNIF board name is DREAMTECH01, without prefix.
Mirroring is hard-wired.
Since the fixed PRG-ROM bank comes from a separate PRG-ROM chip, the ROM file can have a non-power-of-two size.
Mask: $F030
D~[.... BBBB]
++++- PRG A18..14 when CPU A14=0
Note that writes to $5030 are ignored.
Categories: Mappers with CHR RAM