NES 2.0 Mapper 315
NES 2.0 Mapper 315 is used for multicarts using 820732C- and 830134C-numbered PCBs such as 4-in-1 Street Blaster 5. Its UNIF board name is BMC-830134C.
These registers function identically to a normal MMC3, except in GNROM mode.
Mask: probably $E000
D~7654 3210
---------
.... CPpC
|||+- Select 256 KiB outer CHR-ROM bank (i.e. CHR A18)
|++-- Select 128 KiB outer PRG-ROM bank (i.e. PRG A17-A18)
| +-- Select 128 KiB outer CHR-ROM bank (i.e. CHR A17)
+---- Select 64 KiB outer CHR-ROM bank (i.e. CHR A16)
- This bank register functions as a substitute for WRAM and can only be written to if $A001 bit 7 is set and $A001 bit 6 is clear.
- The Outer Bank Register’s PRG A17-A18 replace the MMC3’s, while the Outer Bank Register’s CHR A16 and CHR A17 are OR’d with the respective MMC3 bits.
If PRG A17 and PRG A18 are both 1 (i.e. if $6800 AND $06==$06), standard MMC3 PRG-ROM banking is replaced with an odd GNROM-ish mode, in which the MMC3’s CPU A14 input is held low and PRG A14 is directly connected to CPU A14, resulting in the following bank layout:
- CPU $8000-$BFFF: MMC3 banks effective in the $8000-$BFFF range but as if their bank register values were AND’d with $FD
- CPU $C000-$FFFF: MMC3 banks effective in the $8000-$BFFF range but as if their bank register values were OR’d with $02
NES 2.0 Mapper 348 is similar but with the Outer Bank Register bits being arranged slightly differently.