INES Mapper 034: Difference between revisions
(Rephrase so as not to imply that implementing both sets of regs is the current best practice) |
Rainwarrior (talk | contribs) (older is not the right word either (several current emulators do this), maybe what we need is a warning for developers) |
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[[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. | [[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 [[NES 2.0 submappers#iNES Mapper 034|submapper]] can be used to force use of NINA-001 behavior even with 8 KiB of CHR ROM or CHR RAM. | 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#iNES Mapper 034|submapper]] can be used to force use of NINA-001 behavior even with 8 KiB of CHR ROM or CHR RAM. | ||
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. | |||
== BNROM == | == BNROM == | ||
Revision as of 21:17, 18 March 2014
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 NINA-001 behavior even with 8 KiB of CHR ROM or CHR RAM.
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.
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)
- Darkseed
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: 32 KB ROM
- CHR bank size: 4 KB
- Nametable mirroring: hardwired to horizontal 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
