INES Mapper 034: Difference between revisions
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Many emulators implement both sets of registers simultaneously, which is safe for the two existing commercial games. | Many emulators implement both sets of registers simultaneously, which is safe for the two existing commercial games. | ||
If the emulator wishes to separate the two implementations, they may check the number of CHR banks present: BNROM should be used when there is 0 to 8 KiB of CHR, and NINA-001 should be used otherwise. The [[NES 2.0]] header with a [[ | If the emulator wishes to separate the two implementations, they may check the number of CHR banks present: BNROM should be used when there is 0 to 8 KiB of CHR, and NINA-001 should be used otherwise. The [[NES 2.0]] header with a [[NES_2.0_submappers#034:_BNROM_/_NINA-001|submapper]] can be used to force use of specific board behavior. | ||
Developers wishing to use mapper 34 should strictly use only the BNROM or only the NINA-001 registers in a single ROM, and be careful not to accidentally write to the other set of registers. | Developers wishing to use mapper 34 should strictly use only the BNROM or only the NINA-001 registers in a single ROM, and be careful not to accidentally write to the other set of registers. | ||
[[iNES Mapper 241]] is a variation of BxROM with 8k PRG-RAM at $6000, which avoids having the conflicting NINA-001 registers in that location. | |||
== BNROM == | == BNROM == | ||
| Line 39: | Line 41: | ||
* CHR ROM capacity: 64 KB ROM | * CHR ROM capacity: 64 KB ROM | ||
* CHR bank size: 4 KB | * CHR bank size: 4 KB | ||
* Nametable [[mirroring]]: | * Nametable [[mirroring]]: Hardwired to vertical mirroring | ||
* Subject to [[bus conflict]]s: No | * Subject to [[bus conflict]]s: No | ||
| Line 45: | Line 47: | ||
* ''Impossible Mission 2'' | * ''Impossible Mission 2'' | ||
Registers | Registers: | ||
7 bit 0 | 7 bit 0 | ||
--------- | --------- | ||
Latest revision as of 08:19, 10 January 2024
iNES Mapper 034 is used to designate both the BNROM and NINA-001 boards. These two boards are unrelated, but have unfortunately been grouped into the same mapper.
Many emulators implement both sets of registers simultaneously, which is safe for the two existing commercial games.
If the emulator wishes to separate the two implementations, they may check the number of CHR banks present: BNROM should be used when there is 0 to 8 KiB of CHR, and NINA-001 should be used otherwise. The NES 2.0 header with a submapper can be used to force use of specific board behavior.
Developers wishing to use mapper 34 should strictly use only the BNROM or only the NINA-001 registers in a single ROM, and be careful not to accidentally write to the other set of registers.
iNES Mapper 241 is a variation of BxROM with 8k PRG-RAM at $6000, which avoids having the conflicting NINA-001 registers in that location.
BNROM
See: BNROM
- PRG ROM size: 128 KB (mapper implementations may support up to 512 KB or 8 MB)
- PRG ROM bank size: 32 KB
- PRG RAM: None
- CHR capacity: 8 KB RAM
- CHR bank size: Not bankswitched
- Nametable mirroring: Solder pads select vertical or horizontal mirroring
- Subject to bus conflicts: Yes
Games:
- Deadly Towers (Mashou)
Registers:
7 bit 0
---------
$8000-FFFF: .... ..PP - Select 32 KB PRG ROM bank
Emulators commonly support either a 4-bit or 8-bit register, enabling up to 512 KB or 8 MB PRG ROM. This variant may be referred to as BxROM.
NINA-001
See: NINA-001
- PRG ROM size: 64 KB
- PRG ROM bank size: 32 KB
- PRG RAM: 8 KB, not battery backed
- CHR ROM capacity: 64 KB ROM
- CHR bank size: 4 KB
- Nametable mirroring: Hardwired to vertical mirroring
- Subject to bus conflicts: No
Games:
- Impossible Mission 2
Registers:
7 bit 0
---------
$7FFD: .... ...P - Select 32 KB PRG ROM bank
$7FFE: .... CCCC - Select 4 KB CHR bank at $0000
$7FFF: .... CCCC - Select 4 KB CHR bank at $1000
See also
- Comprehensive NES Mapper Document by \Firebug\, information about mapper's initial state is inaccurate.
