VRC2

The Konami VRC2 is an ASIC mapper.

Overview

• PRG ROM bank size: 8 KB at $8000, and $A000
• PRG RAM: Unknown (none?)
• CHR bank size: 1 KB
• Nametable mirroring: Controlled by mapper
• Subject to bus conflicts: No

The Konami VRC2 is almost identical to the VRC4, but a bit more limited.

Revisions

This mapper had two known revisions: VRC2a and VRC2b. Both revisions uses Address lines A0, A1, and A12-A15 for registers, however VRC2a has A0 and A1 "backwards" from the norm. Address $x001 on VRC2b would be $x002 on VRC2a, and $x002 on VRC2b would be $x001 on VRC2a.

Additionally, VRC2a has 7-bit wide CHR registers, whereas VRC2b has 8-bit wide CHR registers.

This page lists registers as they are in the VRC2b variant. For VRC2a registers, reverse A0 and A1 lines.

Registers

PRG Select 0 ($8000, $8001, $8002, $8003)

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

PRG Select 1 ($A000, $A001, $A002, $A003)

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

Mirroring Control ($9000, $9001, $9002, $9003)

7  bit  0
---------
.... ..MM
       ||
       ++- Mirroring (0: vertical; 1: horizontal;
                          2: one-screen, lower bank; 3: one-screen, upper bank;)

CHR Select 0 ($B000 + $B001)

  $B000        $B001
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $0000
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 1 ($B002 + $B003)

  $B002        $B003
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $0400
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 2 ($C000 + $C001)

  $C000        $C001
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $0800
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 3 ($C002 + $C003)

  $C002        $C003
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $0C00
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 4 ($D000 + $D001)

  $D000        $D001
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $1000
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 5 ($D002 + $D003)

  $D002        $D003
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $1400
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 6 ($E000 + $E001)

  $E000        $E001
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $1800
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)

CHR Select 7 ($E002 + $E003)

  $E002        $E003
7  bit  0    7  bit  0
---------    ---------
.... LLLL    .... HHHH
     ||||         ||||
     ||||         ++++- High 4-bits of 1 KB CHR bank at PPU $1C00
     ++++-------------- Low 4-bits

Note: On VRC2a, the low bit is ignored (right shift value by 1)