INES Mapper 038: Difference between revisions

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(GNROM-like implies Discrete Logic. Also refile in categories. Reformat to standard presentation.)
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[[Category:GNROM-like mappers]][[Category:iNES Mappers]][[Category:Discrete logic mappers]][[Category:in NesCartDB]]
[[Category:GNROM-like mappers|038]][[Category:iNES Mappers|038]][[Category:in NesCartDB|038]]
[[iNES Mapper 038]] represents the board used for Crime Busters. It is another mapper very similiar to [[GxROM|GNROM]] ([[iNES Mapper 066|66]]) except the bits and writeable port moved around.
[[iNES Mapper 038]] represents the board used for Crime Busters. It is another mapper almost identical to [[GxROM|GNROM]] ([[iNES Mapper 066|66]]) except the bits and writeable port moved around.


In [[iNES Mapper DischDocs|Disch's style]]:
== Overview ==
  $7000-$7FFF: [.... CCPP]
* PRG ROM size: 128 KiB
  P = Selects 32kB PRG @ $8000
* PRG ROM bank size: 32 KiB
  C = Selects 8kB CHR @ $0000
* PRG RAM: Impossible
* CHR capacity: 32 KiB ROM
* CHR bank size: 8 KiB
* Nametable mirroring: Hardwired vertical mirroring
* Subject to [[bus conflict]]s: no


Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The [[74138]] used by this board uses /PRGSEL and R/W on its enable inputs, but /PRGSEL is 1 while M2 is low, not just while M2 and A15 are high. As a result, before M2 is high, if the 2A03's A14, A13, and A12 lines are 1 and R/W is 0, the [[74161]]'s /LOAD line will still load from the data bus.
== Registers ==
=== Bank Select ($7000-$7FFF) ===
7  bit  0
---- ----
xxxx CCPP
      ||||
      ||++- Select 32 KB PRG ROM bank for CPU $8000-$FFFF
      ++--- Select 8 KB CHR ROM bank for PPU $0000-$1FFF


Emulator oversize support:
== Hardware ==
Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The [[74138]] used by this board uses /ROMSEL and R/W on its enable inputs, but /ROMSEL is 1 while M2 is low, not just while M2 is high and and A15 is low. As a result, before M2 is high, if the 2A03's A14, A13, and A12 lines are 1 and R/W is 0, the [[74161]]'s /LOAD line will still load from the data bus.
 
== Emulator oversize support ==
   FCEUX (2.1.5):
   FCEUX (2.1.5):
   $7000-$7FFF: [CCCC CCPP]
   $7000-$7FFF: [CCCC CCPP]

Revision as of 21:46, 27 July 2012

iNES Mapper 038 represents the board used for Crime Busters. It is another mapper almost identical to GNROM (66) except the bits and writeable port moved around.

Overview

  • PRG ROM size: 128 KiB
  • PRG ROM bank size: 32 KiB
  • PRG RAM: Impossible
  • CHR capacity: 32 KiB ROM
  • CHR bank size: 8 KiB
  • Nametable mirroring: Hardwired vertical mirroring
  • Subject to bus conflicts: no

Registers

Bank Select ($7000-$7FFF)

7  bit  0
---- ----
xxxx CCPP
     ||||
     ||++- Select 32 KB PRG ROM bank for CPU $8000-$FFFF
     ++--- Select 8 KB CHR ROM bank for PPU $0000-$1FFF

Hardware

Writes to $F000-$FFFF are very likely to also trigger a bankswitch, but well behaved code has no reason to. The 74138 used by this board uses /ROMSEL and R/W on its enable inputs, but /ROMSEL is 1 while M2 is low, not just while M2 is high and and A15 is low. As a result, before M2 is high, if the 2A03's A14, A13, and A12 lines are 1 and R/W is 0, the 74161's /LOAD line will still load from the data bus.

Emulator oversize support

 FCEUX (2.1.5):
  $7000-$7FFF: [CCCC CCPP]

 Nestopia (1.4.0h):
  $6000-$7FFF: [CCCC CC..]
               [PPPP PPPP]
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