NES 2.0 Mapper 375
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iNES Mapper 375 denotes an address-latch-based multicart circuit board mounting 2 MiB of PRG-ROM plus 8 KiB of unbanked CHR-RAM. It is basically an enhancement of INES Mapper 227 that increases the PRG-ROM size to 2 MiB and allows the UNROM-like switchable bank to be changed via a data latch like a normal UNROM board.
Address Latch ($8000-$FFFF, write)
[A~1... UQLQ OQQP PpMS]
|||| |||| |||+-0: PRG A14=p
|||| |||| ||| 1: PRG A14=CPU A14
|||| |||| ||+- 0: Vertical mirroring
|||| |||| || 1: Horizontal mirroring
|||| |||+-++-- PRG A16..A14 (inner bank)
|+|+-|++------ PRG A20..A17 (outer bank)
| | +-------- 0: When CPU A14=1: PRG A16..14=LLL
| | 1: When CPU A14=1: PRG A16..14=PPp
| +----------- Value for PRG A16..14 when CPU A14=1 and O=0
+------------- 0: Address latch writable, PRG A16..A14 normal
1: Address latch locked, PRG A16..A14 from CBA
Power-on value: 0
UNROM-like Data Latch ($8000-$FFFF, write)
[D~.... .CBA]
+++- PRG A16..A14 when U=1 and CPU A14=0
Effective banking modes
Bit 11 Bit 9 Bit 7 Bit 0 Meaning $800s $200s $080s $001s (U) (L) (O) (S) 0 0 0 0 Switchable inner 16 KiB bank PPp at CPU $8000-$BFFF, fixed inner bank #0 at CPU $C000-$FFFF (UNROM-like with fixed bank 0) 0 0 0 1 Switchable inner 16 KIB bank PP0 at CPU $8000-$BFFF, fixed inner bank #0 at CPU $C000-$FFFF (UNROM-like with only even banks reachable, pointless) 0 1 0 0 Switchable inner 16 KiB bank PPp at CPU $8000-$BFFF, fixed inner bank #7 at CPU $C000-$FFFF (UNROM via address latch) 0 1 0 1 Switchable inner 16 KIB bank PP0 at CPU $8000-$BFFF, fixed inner bank #7 at CPU $C000-$FFFF (UNROM via address latch with only even banks reachable, pointless) 0 ? 1 0 Switchable 16 KiB inner bank PPp at CPU $8000-$BFFF, mirrored at CPU $C000-$FFFF (NROM-128) 0 ? 1 1 Switchable 32 KiB inner bank PP at CPU $8000-$FFFF (NROM-256) 1 0 0 0 Switchable inner 16 KiB bank CBA at CPU $8000-$BFFF, fixed inner bank #0 at CPU $C000-$FFFF (UNROM-like with fixed bank 0) 1 0 0 1 Switchable inner 16 KIB bank CB0 at CPU $8000-$BFFF, fixed inner bank #0 at CPU $C000-$FFFF (UNROM-like with only even banks reachable, pointless) 1 1 0 0 Switchable inner 16 KiB bank CBA at CPU $8000-$BFFF, fixed inner bank #7 at CPU $C000-$FFFF (UNROM via data latch) 1 1 0 1 Switchable inner 16 KIB bank CB0 at CPU $8000-$BFFF, fixed inner bank #7 at CPU $C000-$FFFF (UNROM via data latch with only even banks reachable, pointless)
- CHR-RAM is write-protected when O=1 and write-enabled when O=0, i.e. write-protected in the NROM-128 and NROM-256 modes.
- Because all bits are cleared on reset, both CPU $8000-$BFFF and $C000-$FFFF are set to 16 KiB bank #0 on reset.
Similar mappers
- INES Mapper 227 is a variant with only up to 1 MiB PRG-ROM without the data latch.
- INES Mapper 242 is a variant with only up to 512 KiB PRG-ROM without the data latch that moves the m bit to a different bit location. A variant with two PRG-ROM chips exists as well.
- NES 2.0 Mapper 380 is an incompatible variant without the data latch.
- NES 2.0 Mapper 449 is an incompatible variant whose data latch is for 32 KiB CHR-RAM bankswitching functionality instead.
