VRC6

The Konami's VRC6 ASIC mapper comes in two variants. The register descriptions given here are as they exist in Akumajou Densetsu (iNES mapper 024). The A0 and A1 lines are switched in Madara and Esper Dream 2 (iNES mapper 026), so for those games, adjustments will need to be made ($x001 becomes $x002 and vice versa).

Overview

PRG ROM size: Up to 256 KB
PRG ROM bank size: 16 KB at $8000, 8 KB at $C000
PRG RAM: Up to 8 KB
CHR capacity: Up to 256 KB ROM
CHR bank size: 1 KB
Nametable mirroring: Controlled by mapper
Subject to bus conflicts: No

Registers

Only address lines 0, 1, and 12-15 are used for registers, therefore mirrors can be found by ANDing the address with $F003 ($DE6A mirrors $D002)

16k PRG Select ($8000-$8003)

7  bit  0
---------
PPPP PPPP
|||| ||||
++++-++++- Select 16 KB PRG ROM at $8000

8k PRG Select ($C000-$C003)

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

Mirroring Control ($B003)

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

CHR Select 0 ($D000)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $0000

CHR Select 1 ($D001)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $0400

CHR Select 2 ($D002)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $0800

CHR Select 3 ($D003)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $0C00

CHR Select 4 ($E000)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $1000

CHR Select 5 ($E001)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $1400

CHR Select 6 ($E002)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $1800

CHR Select 7 ($E003)

7  bit  0
---------
CCCC CCCC
|||| ||||
++++-++++- Select 1 KB CHR ROM at PPU $1C00

IRQ control ($F00x)

$F000:  IRQ Latch
$F001:  IRQ Control
$F002:  IRQ Acknowledge

Many VRC mappers use the same IRQ system. For details on IRQ operation, see VRC IRQs.

Sound ($900x, $A00x, $B000-$B002)

For details on sound information, see VRC6 audio.