INES Mapper 074: Difference between revisions

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(misheadered m74 games weren't all m192...)
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{{DEFAULTSORT:074}}[[Category:iNES Mappers]][[Category:MMC3 with CHR ROM and CHR RAM]][[Category:Mappers with scanline IRQs]]
{{DEFAULTSORT:074}}[[Category:iNES Mappers]][[Category:MMC3 with CHR ROM and CHR RAM]][[Category:Mappers with scanline IRQs]]
'''iNES Mapper 074''' is a [[MMC3]] clone used in Eastern games.
'''iNES Mapper 074''' denotes the '''43-393'''/'''43-406'''/'''860908C''' PCB, used by several games from Waixing:
It's identical to [[iNES Mapper 192]] and used for the same reason, except that only pages 8 and 9 are RAM.
* ''機甲戰士'' (Jījiǎ Zhànshì, Chinese translation of Data East's ''Metal Max'')
If the [[NES 2.0]] header is present, 74 and 192 should be emulated identically, as NES 2.0 specifies CHR RAM size elsewhere.
* ''甲A - China Soccer League for Division A''
* ''第四次: 机器人大战 - Robot War IV''
* ''風雲 - Traitor Legend'' (original 1997 version)
The circuit board mounts an [[MMC3]] clone together with a 74LS138 and 74LS139 to redirect 1 KiB CHR-ROM banks #8 and #9 to 2 KiB of CHR-RAM.


BizHawk supports this mapper as of r3973; FCEUX and FCEU-MM have supported them for a long time but definitely as of 26-nov-2012, although CRC checks for m192<->m074 may be lacking.
=Notes=
 
* SMYNES and older versions of VirtuaNES EX/Plus use mapper 74 to denote ''any'' MMC3-based mixed CHR-ROM/CHR-RAM game by simply making ''all'' of CHR-ROM writable, even if those games actually use [[iNES Mapper 191|191]], [[iNES Mapper 192|192]], [[iNES Mapper 194|194]], or [[iNES Mapper 195|195]]. This approach fails in the case of ''甲A - China Soccer League for Division A'', as the game writes all zeros to whatever CHR-ROM banks are mapped at power-on, overwriting CHR-ROM data in the process. As a result, the publicly available dump of that game (PRG-ROM CRC32 0x78FB3ED6) has been modified to remove those writes.
Many games are mis-headered as m074 but should really be one of m191, m192, m194, or m195 and will either need to be changed to the correct mapper, or changed to the correct amount of CHR RAM and handled by unified code.
* Nestopia emulates all of Waixing's MMC3 clones with a slight variation on the mirroring control register at $A000, additionally treating a written value of 2 or 3 as 1scA and 1scB mirroring respectively.
 
* [[iNES Mapper 119]] is Nintendo's first-party analog. Mappers [[iNES Mapper 252|252]] and [[iNES Mapper 253|253]], also used for Waixing's localizations, are similar but use a VRC4.
  Here are Disch's original notes:
  ========================
  =  Mapper 074          =
  ========================
 
 
  aka:
  --------------------------
  Pirate MMC3 variant
 
 
  Example Games:
  --------------------------
  Di 4 Ci - Ji Qi Ren Dai Zhan
  Ji Jia Zhan Shi
 
 
  Notes:
  --------------------------
  This mapper is a modified MMC3 (or is based on MMC3?).
 
  In addition to any CHR-ROM present, there is also an additional 2k of CHR-RAM which is selectable. CHR pages
  $08 and $09 select CHR-RAM, other pages select CHR-ROM
 
  Apart from that, this mapper behaves exactly like your typical MMC3.  See mapper 004 for details.

Latest revision as of 09:20, 22 December 2023

iNES Mapper 074 denotes the 43-393/43-406/860908C PCB, used by several games from Waixing:

  • 機甲戰士 (Jījiǎ Zhànshì, Chinese translation of Data East's Metal Max)
  • 甲A - China Soccer League for Division A
  • 第四次: 机器人大战 - Robot War IV
  • 風雲 - Traitor Legend (original 1997 version)

The circuit board mounts an MMC3 clone together with a 74LS138 and 74LS139 to redirect 1 KiB CHR-ROM banks #8 and #9 to 2 KiB of CHR-RAM.

Notes

  • SMYNES and older versions of VirtuaNES EX/Plus use mapper 74 to denote any MMC3-based mixed CHR-ROM/CHR-RAM game by simply making all of CHR-ROM writable, even if those games actually use 191, 192, 194, or 195. This approach fails in the case of 甲A - China Soccer League for Division A, as the game writes all zeros to whatever CHR-ROM banks are mapped at power-on, overwriting CHR-ROM data in the process. As a result, the publicly available dump of that game (PRG-ROM CRC32 0x78FB3ED6) has been modified to remove those writes.
  • Nestopia emulates all of Waixing's MMC3 clones with a slight variation on the mirroring control register at $A000, additionally treating a written value of 2 or 3 as 1scA and 1scB mirroring respectively.
  • iNES Mapper 119 is Nintendo's first-party analog. Mappers 252 and 253, also used for Waixing's localizations, are similar but use a VRC4.
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