NES 2.0 Mapper 514

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NES 2.0 Mapper 514 is used for the game 小霸王 卡拉OK (Subor Karaoke). It banks PRG-ROM in 32 KiB amounts, has 8 KiB WRAM, and 2x4 KiB of CHR-RAM that can be bankswitched according to the current nametable offset during rendering.

Mode/PRG-ROM Bank Register ($8000)

Bit 7654 3210
    BMPP PPPP
    ||++-++++- Select 32 KiB PRG-ROM bank at CPU $8000
    |+-------- Select nametable mirroring
    |           0: Vertical
    |           1: Horizontal
    +--------- Select CHR-RAM banking mode (during PPU read accesses only)
                0: 8 KiB CHR-RAM at PPU $0000-$1FFF
                1: 4 KiB CHR-RAM at PPU $0000-$0FFF automatically switched, 4 KiB CHR-RAM at PPU $1000-$1FFF fixed to second half of CHR-RAM

Notes

  • When Bit 7 is set, PPU $0000-$0FFF will point to the first half of CHR-RAM while the PPU renders from the first CIRAM nametable, and the second half of CHR-RAM while the PPU renders from the second CIRAM nametable (offset $2400/$2C00 with vertical mirroring, or offset $2800/$2C00 with horizontal mirroring). The game uses this feature to have a CHR bankswitch in the middle of the screen by setting the scroll value such that the position at which the CHR bank needs to be switched is the seams between the two CIRAM nametables. This works even in the horizontal direction, providing a simple way for a mid-scanline bankswitch. Note that write accesses to CHR-RAM are never bankswitched.
  • Note that this game requires Dendy video timing and will produce graphical glitches with NTSC or regular PAL timing.