INES Mapper 178: Difference between revisions

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(On second thought, take the Jncota variant out of mapper 178, since it uses hard-wired mirroring and would require an ugly heuristic otherwise.)
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{{DEFAULTSORT:178}}[[Category:iNES Mappers]][[Category:Mappers using $4020-$5FFF]][[Category:Mappers with large PRG RAM]]'''iNES Mapper 178''' is used by some games from Waixing (on a PCB named '''FS305'''), Nanjing (on a PCB named '''NJ0430'''), Jncota and Henge Dianzi as well as some educational computers from GameStar, a.k.a. Belsonic. The chipset is designed for using 8 KiB of chip-internal unbanked CHR-RAM, but can address external RAM as well, banked in 8 KiB amounts, which can be connected on the circuit board as PRG-RAM, CHR-RAM or CHR-ROM.  
{{DEFAULTSORT:178}}[[Category:iNES Mappers]][[Category:Mappers using $4020-$5FFF]][[Category:Mappers with large PRG RAM]]'''iNES Mapper 178''' is used by some games from Waixing (on a PCB named '''FS305'''), Nanjing (on a PCB named '''NJ0430'''), Jncota and Henge Dianzi as well as some educational computers from GameStar, a.k.a. Belsonic. The chipset is designed for using 8 KiB of chip-internal unbanked CHR-RAM, but can address external RAM/ROM as well, banked in 8 KiB amounts. Circuit boards described by iNES Mapper 178 connect external RAM as bankable PRG-RAM mapped to CPU $6000-$7FFF.


=Banks=
* CPU $6000-$7FFF: 8 KiB switchable PRG-RAM bank
* CPU $8000-$FFFF: 16/32 KiB PRG-ROM bank, switchable
* PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM
* Nametable mirroring: Switchable horizontal/vertical settings
=Registers=
=Registers=
==Mode Register ($4800)==
==Mode Register ($4800)==
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This can be considered an outer bank register for UNROM mode.
This can be considered an outer bank register for UNROM mode.
==External RAM/ROM Bank Register ($4803) ==
==PRG-RAM Bank register ($4803) ==
  7654 3210
  7654 3210
  ---------
  ---------
  BBBB BBBB
  BBBB BBBB
  ++++-++++- External A20..A13
  ++++-++++- PRG-RAM A20?..A13
 
PRG-RAM is mapped to CPU $6000-$7FFF and is banked in 8 KiB amounts.


If a cartridge has CHR-ROM, this register selects the 8 KiB CHR-ROM bank, otherwise it selects an 8 KiB PRG-RAM bank at CPU $6000-$7FFF.
==Infrared==
==Infrared==
Some cartridges have an additional infrared sensor. Infrared receiving is working by having two registers:
Some cartridges have an additional infrared sensor. Infrared receiving is working by having two registers:

Revision as of 18:40, 4 November 2019

iNES Mapper 178 is used by some games from Waixing (on a PCB named FS305), Nanjing (on a PCB named NJ0430), Jncota and Henge Dianzi as well as some educational computers from GameStar, a.k.a. Belsonic. The chipset is designed for using 8 KiB of chip-internal unbanked CHR-RAM, but can address external RAM/ROM as well, banked in 8 KiB amounts. Circuit boards described by iNES Mapper 178 connect external RAM as bankable PRG-RAM mapped to CPU $6000-$7FFF.

Banks

  • CPU $6000-$7FFF: 8 KiB switchable PRG-RAM bank
  • CPU $8000-$FFFF: 16/32 KiB PRG-ROM bank, switchable
  • PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM
  • Nametable mirroring: Switchable horizontal/vertical settings

Registers

Mode Register ($4800)

7654 3210
---------
.... .SSM
      ||+- Nametable mirroring
      ||    0: Vertical
      ||    1: Horizontal
      ++-- PRG banking mode
            0: NROM-256/BNROM (PRG A14=CPU A14)
            1: UNROM (PRG A14..16=111b if CPU A14=1)
            2: NROM-128
            3: UNROM but with bit 0 of "fixed" bank selectable
               (PRG A15..16=11b if CPU A14=1)

Low PRG Bank Register ($4801)

7654 3210
---------
.... .LLL
      +++- PRG A16..A14

This can be considered an inner bank register for UNROM mode.

High PRG Bank Register ($4802)

7654 3210
---------
HHHH HHHH
++++-++++- PRG A24?..A17

This can be considered an outer bank register for UNROM mode.

PRG-RAM Bank register ($4803)

7654 3210
---------
BBBB BBBB
++++-++++- PRG-RAM A20?..A13

PRG-RAM is mapped to CPU $6000-$7FFF and is banked in 8 KiB amounts.

Infrared

Some cartridges have an additional infrared sensor. Infrared receiving is working by having two registers:

 $5000-$5FFF:  [.... ...V]  (read only)
    V = read current bit from IR sensor
 $6000-$7FFF:  [I... ....]  (write only)
    I = set to activate interrupts by infrared signal

Errata

  • The commonly-available ROM images of
    • 宠物: 小精灵 IV (Chǒngwù: Xiǎo Jīnglíng IV), headerless CRC32 0xB0B13DBD
    • Education Computer 32-in-1 (Game Star) [!], headerless CRC32 0xF834F634
will not work when emulated using the above description. The meaning of registers $4801 and $4802 is swapped, and an emulator must shift the value of $4802 one bit to the left before ORing with $4801. While it cannot be ruled out that these games use an alternative version of the hardware, the more likely explanation is that these are simply bad dumps (notwithstanding GoodNES 3.23b's [!] tag) where the dumper confused the two bank registers.
  • Supposedly, the new PRG bank is only committed when $4801 is written. Emulating this supposed behavior however will break Ping Pong, while commiting the PRG bank after any $480x write does not seem to break anything else.
  • Most of the educational computers using this mapper require Dendy video timing and will freeze at various points when run with NTSC timing.
  • The Waixing FS305 circuit board connects PRG A14 directly to CPU A14, making all PRG banking modes except BNROM unusable. Since it writes the correct banking mode to $4800, it does not require any special treatment.

See also