INES Mapper 078: Difference between revisions

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(Created page with "Category:iNES Mappers Here are Disch's original notes: ======================== = Mapper 078 = ======================== Example Games: ---------…")
 
(→‎Bank Select ($8000-$FFFF): it's apparently not the "four screens" nametables bit.)
 
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[[Category:iNES Mappers]]
{{DEFAULTSORT:078}}[[Category:iNES Mappers]][[Category:Discrete logic mappers]][[Category:in NesCartDB]][[Category:NES 2.0 mappers with submappers]]
  Here are Disch's original notes: 
[[iNES Mapper 078]] was used for two games: ''Holy Diver'' and ''Uchuusen - Cosmo Carrier''.
  ========================
 
  =  Mapper 078          =
== Overview ==
  ========================
* PRG ROM size: 128 KiB
 
* PRG ROM bank size: 16 KiB
 
* PRG RAM: No
  Example Games:
* CHR capacity: 128KiB ROM
  --------------------------
* CHR bank size: 8 KiB
  Holy Diver
* Nametable mirroring: Mapper controlled
  Uchuusen - Cosmo Carrier
* Subject to [[bus conflict]]s: Yes
 
 
 
== Banks ==
  Notes:
* CPU $8000-$BFFF: 16KiB switchable PRG ROM bank
  ---------------------------
* CPU $C000-$FFFF: Fixed to last 16KiB of PRG ROM
  This mapper number covers two seperate mappers which are *almost* identical... however the mirroring control
* PPU $0000-$1FFF: 8KiB switchable CHR ROM bank
  on each is different (making them incompatible)You'll probably have to do a CRC or Hash check to figure
 
  out which mirroring setup to use.
== Registers ==
 
=== Bank Select ($8000-$FFFF) ===
  I think some emus might also look at the mirroring bit in the iNES header to determine which setup to use --
7  bit  0
  however the ROMs I have do not seem to have the mirroring bit set differently, so I don't know how well that
---- ----
  would work (not to mention it's probably not a good idea anyway).
CCCC MPPP
 
|||| ||||
  I'm unsure whether or not this mapper suffers from bus conflicts. Use caution!
|||| |+++-- Select 16 KiB PRG ROM bank for CPU $8000-$BFFF
 
|||| +----- Mirroring.  Holy Diver: 0 = H, 1 = V.  Cosmo Carrier: 0 = 1scA, 1 = 1scB.
 
++++------- Select 8KiB CHR ROM bank for PPU $0000-$1FFF
  Registers:
 
  ---------------------------
The two mirroring modes are not compatible, and trying to run either game with the other's hardware will produce major graphical glitching or lockups.
 
 
    $8000-FFFF:  [CCCC MPPP]
iNES1 ROM image headers often set the "alternative nametables" flag for Holy Diver and cleared it for Cosmo Carrier. NES2.0 uses submappers.
      C = CHR Reg (8k @ $0000)
 
      P = PRG Reg (16k @ $8000)
== Hardware ==
      M = Mirroring:
 
 
In both cases, the hardware implementation is simply a [[CNROM]] and a [[UNROM]] put togetherTwo [[74161|74HC161]] are used to form an 8 bit latch, with 4 bits connecting the CHR ROM's high address lines, and 3 bits connecting to a [[7432|74HC32]], which provides the logic to fix the top bank of PRG ROM while swapping the first 16KiB. The last latched bit is connected directly to CIRAM A10 on Cosmo Carrier, as in [[AxROM]].  On Holy Diver, that bit is connected to a [[7400|74HC00]], which serves as a 2:1 mux of PPU A10 and PPU A11 into CIRAM A10 to provide the desired mirroring.  Holy Diver also contains a 74HC245 to compensate for a slow CHR ROM chip.
        --For Uchuusen - Cosmo Carrier--
 
          0 = 1ScA
For homebrew, both Nestopia-1.4.0 and FCEUX-2.1.5 default to the 1scA/1scB mirroring provided by Uchuusen.
          1 = 1ScB
Emulators SHOULD support [[NES 2.0 submappers]]: 1 for Uchuusen and 3 for Holy Diver.
 
 
        --For Holy Diver--
== See also ==
          0 = Horz
* [http://www.romhacking.net/documents/362/ NES Mapper list] by Disch.
          1 = Vert
*[http://nesdev.org/mappers.zip Comprehensive NES Mapper Document] by \Firebug\. Information on mapper's initial state is innacurate.
 
 
 
[[Category:NES 2.0 mappers with submappers]]
  PRG Setup:
  ---------------------------
 
        $8000  $A000  $C000  $E000 
      +---------------+---------------+
      |    $8000    |    { -1}    |
      +---------------+---------------+

Latest revision as of 09:43, 1 February 2024

iNES Mapper 078 was used for two games: Holy Diver and Uchuusen - Cosmo Carrier.

Overview

  • PRG ROM size: 128 KiB
  • PRG ROM bank size: 16 KiB
  • PRG RAM: No
  • CHR capacity: 128KiB ROM
  • CHR bank size: 8 KiB
  • Nametable mirroring: Mapper controlled
  • Subject to bus conflicts: Yes

Banks

  • CPU $8000-$BFFF: 16KiB switchable PRG ROM bank
  • CPU $C000-$FFFF: Fixed to last 16KiB of PRG ROM
  • PPU $0000-$1FFF: 8KiB switchable CHR ROM bank

Registers

Bank Select ($8000-$FFFF)

7  bit  0
---- ----
CCCC MPPP
|||| ||||
|||| |+++-- Select 16 KiB PRG ROM bank for CPU $8000-$BFFF
|||| +----- Mirroring.  Holy Diver: 0 = H, 1 = V.  Cosmo Carrier: 0 = 1scA, 1 = 1scB.
++++------- Select 8KiB CHR ROM bank for PPU $0000-$1FFF

The two mirroring modes are not compatible, and trying to run either game with the other's hardware will produce major graphical glitching or lockups.

iNES1 ROM image headers often set the "alternative nametables" flag for Holy Diver and cleared it for Cosmo Carrier. NES2.0 uses submappers.

Hardware

In both cases, the hardware implementation is simply a CNROM and a UNROM put together. Two 74HC161 are used to form an 8 bit latch, with 4 bits connecting the CHR ROM's high address lines, and 3 bits connecting to a 74HC32, which provides the logic to fix the top bank of PRG ROM while swapping the first 16KiB. The last latched bit is connected directly to CIRAM A10 on Cosmo Carrier, as in AxROM. On Holy Diver, that bit is connected to a 74HC00, which serves as a 2:1 mux of PPU A10 and PPU A11 into CIRAM A10 to provide the desired mirroring. Holy Diver also contains a 74HC245 to compensate for a slow CHR ROM chip.

For homebrew, both Nestopia-1.4.0 and FCEUX-2.1.5 default to the 1scA/1scB mirroring provided by Uchuusen. Emulators SHOULD support NES 2.0 submappers: 1 for Uchuusen and 3 for Holy Diver.

See also