NES 2.0 Mapper 269

NES 2.0 Mapper 269 is used for at least one plug-and-play console and two multicarts with an MMC3 clone and four additional outer bank registers:

• Games Xplosion 121-in-1
• 15000-in-1
• 18000-in-1

PRG and CHR fetches are mapped to different areas of a single address space, similar to the VTxx consoles in OneBus mode. As the plug-and-play console's square wave duty cycles are not reversed however, the actual hardware cannot be VTxx.

Registers

MMC3-compatible registers

Mask: probably $E001

$8000, $8001, $A000, $A001, $C000, $C001, $E000, $E001: As normal MMC3.

Outer bank registers ($5000)

There are four outer bank registers, all of which are accessed at address $5000. The first write goes to the first register, the second write to the second, and so on; the fifth write goes to the first register again.

Mask: unknown, but probably $F008, as a few games' writes to $5008 must be ignored

Register 0:

7654 3210
---------
CCCC CCCC
++++-++++- Bits 0-7 of the 1 KiB Outer CHR Bank number

Register 1:

7654 3210
---------
PPPP PPPP
++++-++++- Bits 0-7 of the 8 KiB Outer PRG Bank number

Register 2:

7654 3210
---------
CCCC MMMM
|||| ++++- Outer CHR Bank mask in number of most significant bits,
||||       e.g. 0=0x00, 1=0x80, 2=0xC0, 3=0xE0, 4=0xF0
++++------ Bits 8-11 of the 1 KiB Outer CHR Bank number

Register 3:

7654 3210
---------
OOMM MMMM
||++-++++- Outer PRG Bank mask (bit mask, not number of bits)
++-------- Bits 8/9 of the 8 KiB Outer PRG Bank number, also
           Bits 12/13 of the 1 KiB Outer CHR Bank number

The final 8 KiB PRG and 1 KiB CHR bank number are therefore:

PRGBank := (MMC3PRGBank &~OuterPRGBankMask) | (OuterPRGBank &OuterPRGBankMask);
CHRBank := (MMC3CHRBank &~OuterCHRBankMask) | (OuterCHRBank &OuterCHRBankMask);

CHR Scrambling

The CHR data is scrambled by changing the bit order.

Stored bit  76543210
            --------
Actual bit  70615243

Which means that to get from the written data to the actual data, the following operation must be performed:

Val =((Val &1) <<6) | ((Val &2) <<3) | ((Val &4) <<0) | ((Val &8) >>3) | ((Val &16) >>3) | ((Val &32) >>2) | ((Val &64) >>1) | ((Val &128) <<0);

Notes

• Initial register values must be 0x00 for registers 0, 1 and 3, and 0x0F for register 2.
• This mapper seems to be an enhanced version of Mapper 45.
• On the Games Xplosion 121-in-1 multicart, game #48 (First Defender) enables interrupts but fails to disable the frame IRQ, freezing on emulators that accurately power-on with the frame IRQ enabled.