VRC1

The Konami VRC1 is an ASIC mapper. The iNES format assigns mapper 75 to VRC1.

The VRC1 was used in several Famicom games released by Konami and Jaleco:

• Exciting Boxing
• Ganbare Goemon! Karakuri Douchuu
• Jajamaru Ninpouchou
• King Kong 2: Ikari no Megaton Punch
• Moero!! Junior Basket: Two on Two
• Tetsuwan Atom

Overview

• PRG ROM size: Up to 128 KiB
• PRG ROM bank size: 8 KiB
• PRG RAM: None
• CHR bank size: 4 KiB
• CHR ROM size: Up to 128 KiB
• Nametable mirroring: Controlled by mapper
• Subject to bus conflicts: No

See VRC1 pinout for chip pinout.

Banks

• CPU $8000-$9FFF: 8 KiB switchable PRG ROM bank
• CPU $A000-$BFFF: 8 KiB switchable PRG ROM bank
• CPU $C000-$DFFF: 8 KiB switchable PRG ROM bank
• CPU $E000-$FFFF: 8 KiB PRG ROM bank, fixed to the last bank
• PPU $0000-$0FFF: 4 KiB switchable CHR bank
• PPU $1000-$1FFF: 4 KiB switchable CHR bank

Registers

PRG Select 0 ($8000-$8FFF)

7  bit  0
---------
.... PPPP
     ||||
     ++++- Select 8 KB PRG ROM at $8000

PRG Select 1 ($A000-$AFFF)

7  bit  0
---------
.... PPPP
     ||||
     ++++- Select 8 KB PRG ROM at $A000

PRG Select 2 ($C000-$CFFF)

7  bit  0
---------
.... PPPP
     ||||
     ++++- Select 8 KB PRG ROM at $C000

Mirroring Control, CHR bits ($9000-$9FFF)

7  bit  0
---------
.... .BAM
      |||
      ||+- Mirroring  (0: Vertical; 1: Horizontal)
      |+-- High Bit of 4 KB CHR bank at PPU $0000
      +--- High Bit of 4 KB CHR bank at PPU $1000

The mirroring bit is ignored if the cartridge is wired for 4-screen VRAM, as is typical for Vs. System games using the VRC1.

CHR Select 0 ($E000-$EFFF)

7  bit  0
---------
.... CCCC
     ||||
     ++++- Low 4 bits of 4 KB CHR bank at PPU $0000

These bits combined with bit 1 of $9000 make a 5-bit CHR selection.

CHR Select 1 ($F000-$FFFF)

7  bit  0
---------
.... CCCC
     ||||
     ++++- Low 4 bits of 4 KB CHR bank at PPU $1000

These bits combined with bit 2 of $9000 make a 5-bit CHR selection.

References

• Disch's Mapper Notes