INES Mapper 074: Difference between revisions

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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 [[iNES Mapper 191|191]], [[iNES Mapper 192|192]], [[iNES Mapper 194|194]], or [[iNES Mapper 195|195]] 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.
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.
 
  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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