NES 2.0 Mapper 551 is a variant of INES Mapper 178 used for several Jncota re-releases of RPG games that were originally published by C&E and Supertone:
Compared to INES Mapper 178, mirroring is hard-wired, and the chipset's internal CHR-RAM is not used in favor of CHR-ROM.
7654 3210
---------
.... .SS.
||
||
||
++-- PRG banking mode
0: NROM-256/BNROM (PRG A14=CPU A14)
1: UNROM (PRG A14..16=111b if CPU A14=1)
2: NROM-128
3: UNROM but with bit 0 of "fixed" bank selectable
(PRG A15..16=11b if CPU A14=1)
7654 3210
---------
.... .LLL
+++- PRG A16..A14
This can be considered an inner bank register for UNROM mode.
7654 3210 --------- HHHH HHHH ++++-++++- PRG A24?..A17
This can be considered an outer bank register for UNROM mode.
7654 3210 --------- BBBB BBBB ++++-++++- CHR-ROM A20?..A13
Categories: Mappers using $4020-$5FFF