INES Mapper 176

iNES Mapper 176 denotes the 8025 enhanced MMC3 chipset. It used by many multicarts, Chinese single-game and educational computer cartridges, and Techno Source’s Intellivision X2 Plug-and-Play console. Incompatible variations exist that are denoted via NES 2.0 Submapper.

• The SFC-12B PCB (submapper 0) mounts both CHR-ROM and CHR-RAM that are selected via $5xx0.5.
• Eight MMC3 PRG bits mean that bit 6 and 7 of $8000.6/7 are applied, and the fixed banks are $FE/$FF rather than $3E/$3F. This implies that the multicart’s reset vector lies at address PRG-ROM address $1FFFFC rather than $7FFFC if the PRG-ROM is that large.

FS005 (Submapper 2) can disable the registers in the $5000-$5FFF range using the RAM Configuration Register ($A001). The same register also enables a mixed CHR-ROM/CHR-RAM mode that is similar to INES Mapper 195.

Mask: $Fxx7 (Submapper 3), $5xx3 (all others), x determined by solder pad setting

7654 3210
---- ----
PCTm PMMM
|||| ||||
|||| |+++- Select PRG Banking Mode (ignored in Extended MMC3 Mode)
|||| |      0: MMC3 PRG Mode, 2 MiB/512 KiB Outer PRG Bank Size
|||| |      1: MMC3 PRG Mode, 256 KiB Outer PRG Bank Size
|||| |      2: MMC3 PRG Mode, 128 KiB Outer PRG Bank Size
|||| |      3: NROM-128 PRG Mode, 16 KiB PRG at $8000-$BFFF mirrored at $C000-$FFFF
|||| |      4: NROM-256 PRG Mode, 32 KiB PRG at $8000-$FFFF
|||| |      5: UNROM PRG Mode, 16 KiB PRG at $8000-$BFFF, inner bank #7 at $C000-$FFFF
|||| |      6-7: Never used
|||| +---- PRG A21 (Submapper 2 only)
|||+------ Select Outer CHR Bank Size
|||         0: In MMC3 CHR Mode: 256 KiB
|||            In CNROM CHR Mode: 32 KiB (Submapper 1 only)
|||         1: In MMC3 CHR Mode: 128 KiB
|||            In CNROM CHR Mode: 16 KiB (Submapper 1 only)
||+------- Submappers 0/1 with both CHR-ROM and CHR-RAM (e.g. SFC-12B PCB):
||          0: Select CHR-ROM
||          1: Select CHR-RAM
||         Submapper 1 with $5xx0.6=1:
||          0: Enable CNROM latch (CNROM mode)
||          1: Disable CNROM latch (NROM mode)
|+-------- CHR A10-12 Mode
|           0: from MMC3
|           1: from PPU
+--------- PRG A22 (Submapper 2 only)

Power-on value: $00

Mask: $Fxx7 (Submapper 3), $Fxx3 (all others), x determined by solder pad setting

7654 3210
---- ----
.PPP PPPP
 ||| ||||
 +++-++++- PRG A20..A14

Power-on value: $00

Depending on the PRG banking mode set via $5xx0, only the higher bits of this register are applied:

PRG A..
21111111
09876543
--------
MMMMMMMM  Submappers 1/3 in PRG Mode 0 (MMC3 2 MiB) or Extended MMC3 Mode
BBMMMMMM  Submappers 0/2/4 in PRG Mode 0 (MMC3 512 KiB)
BBBMMMMM  PRG Mode 1 (MMC3 256 KiB)
BBBBMMMM  PRG Mode 2 (MMC3 128 KiB)
BBBBBBBC  PRG Mode 3 (NROM-128)
BBBBBBCC  PRG Mode 4 (NROM-256)
BBBBLLLC  PRG Mode 5 (UNROM)

M: Bit comes from MMC3 ($8000.6/7 or fixed bank)
B: Bit comes from PRG Base Register ($5xx1)
L: Bit comes from UNROM Latch ($8000-$FFFF or fixed bank)
C: Bit comes from CPU

Submapper 5 only selects PRG A14-A18 (i.e. 512 KiB) via this register, selecting upper PRG bits via register $4800.

Mask: $Fxx7 (Submapper 3), x determined by solder pad setting

7654 3210
---- ----
.... PPPP
     ||||
     ++++- PRG Base A24..A21

Power-on value: $00

Mask: $F800

7654 3210
---- ----
..PP PPPP
  || ||||
  ++-++++- PRG Base A24..A19

Power-on value: $00

Mask: $Fxx7 (Submapper 3), $5xx3 (all others), x determined by solder pad setting

7654 3210
---- ----
ccdC CCCC
|||| ||||
++++-++++- CHR A20..A13
||+------- PRG A25 (Submapper 2 only)
++-------- PRG A24..A23 (Submapper 2 only)
+--------- PRG A21 (Submapper 4)

Power-on value: $00

Depending on the CHR banking mode set via $5xx0, only the higher bits of this register are applied:

CHR A..
21111111111
09876543210
-----------
BBBMMMMMMMM  MMC3 CHR Mode ($5xx0.6=0), 256 KiB ($5xx0.4=0)
BBBBMMMMMMM  MMC3 CHR Mode ($5xx0.6=0), 128 KiB ($5xx0.4=1)
BBBBBBLLPPP  CNROM CHR Mode ($5xx0.6=1, $5xx0.5=0), 32 KiB ($5xx0.4=0), Submapper 1 only
BBBBBBBLPPP  CNROM CHR Mode ($5xx0.6=1, $5xx0.5=0), 16 KiB ($5xx0.4=1), Submapper 1 only
BBBBBBBBPPP  NROM CHR Mode ($5xx0.6=1, $5xx0.5=1 or Submapper other than 1)

M: Bit comes from MMC3 ($8000.0-5)
B: Bit comes from CHR Base Register ($5xx2)
L: Bit comes from CNROM Latch ($8000-$FFFF)
P: Bit comes from PPU

Mask: $Fxx7 (Submapper 3), x determined by solder pad setting

7654 3210
---- ----
.... PPPP
     ||||
     ++++- CHR Base A24..A21

Power-on value: $00

Mask: $Fxx3, x determined by solder pad setting

7654 3210
---- ----
.?.. .?E.
       | 
       +- Extended MMC3 Mode
           0: disable
           1: enable

Power-on value: $00

Most multicarts write value $44 rather than $00 to disable Extended MMC3 Mode. Hardware tests do not indicate any difference in behavior between writing $00 and $44.

Mask: $E003

7654 3210
---- ----
.... ..MM
       ++- Select nametable mirroring 
           0: Vertical
           1: Horizontal
           2: Single-screen, page 0 (Submapper 2 only)
           3: Single-screen, page 1 (Submapper 2 only)
Power-on value: $00

Single-screen mirroring is only available when the RAM Configuration Register is enabled ($A001.5).

Mask: $E003

This register functions like MMC3 register $A001 until bit 5 is set, which turns it into the RAM Configuration Register.

7654 3210
---- ----
RFE. SCWW
|||  ||||
|||  ||++- Select 8 KiB PRG-RAM bank at $6000-$7FFF. Ignored if Bit 5 is clear.
|||  |+--- Select the memory type in the first 8 KiB of CHR space. Ignored if Bit 5 is clear.
|||  |      0: First 8 KiB are CHR-ROM
|||  |      1: First 8 KiB are CHR-RAM
|||  +---- Unknown
||+------- RAM Configuration Register Enable
||          0: RAM Configuration Register disabled, $A001 functions as on MMC3, 8 KiB of WRAM
||          1: RAM Configuration Register enabled, 32 KiB of WRAM
|+-------- Outer Bank Registers Enable. Ignored if Bit 5 is clear.
|           0: Outer Bank Registers disabled, $5000-$5FFF maps to the second 4 KiB of the 8 KiB WRAM bank 2
|           1: Outer Bank Registers enabled in the $5000-$5FFF range
+--------- PRG RAM enable (0: disable, 1: enable)

Power-on value: $00

In UNROM Mode (PRG Mode 5), writing to this address range changes the 16 KiB inner PRG bank at $8000-$BFFF.

In CNROM Mode, writing to this address range changes the inner CHR bank.

Mask: $E003 (verified on real hardware)

Some multicart games depend on writes to $9FFF not doing anything as a result of the MMC3 address mask being $E003 rather than the standard $E001.

If the “Extended MMC3 Mode” bit in register $5xx3 is clear, then these registers function identically to the MMC3. On Submappers 1 and 2, if the “Extended MMC3 Mode” bit is set, four more bank registers become available at $8000/$8001, so that the original two 2 KiB CHR banks become four 1 KiB CHR banks, and the two fixed 8 KiB PRG banks become selectable, similar to the RAMBO-1. Register $8000 if $5xx3 bit 1 is set:

7  bit  0
---- ----
CP.. RRRR
||   ||||
||   ++++- Specify which bank register to update on next write to Bank Data register
||         $0: Select 1 KB CHR bank at PPU $0000-$03FF (or $1000-$13FF)
||         $1: Select 1 KB CHR bank at PPU $0800-$0BFF (or $1800-$1BFF)
||         $2: Select 1 KB CHR bank at PPU $1000-$13FF (or $0000-$03FF)
||         $3: Select 1 KB CHR bank at PPU $1400-$17FF (or $0400-$07FF)
||         $4: Select 1 KB CHR bank at PPU $1800-$1BFF (or $0800-$0BFF)
||         $5: Select 1 KB CHR bank at PPU $1C00-$1FFF (or $0C00-$0FFF)
||         $6: Select 8 KB PRG ROM bank at $8000-$9FFF (or $C000-$DFFF)
||         $7: Select 8 KB PRG ROM bank at $A000-$BFFF
||         $8: Select 8 KB PRG ROM bank at $C000-$DFFF (or $8000-$9FFF)
||         $9: Select 8 KB PRG ROM bank at $E000-$FFFF
||         $A: Select 1 KB CHR bank at PPU $0400-$07FF (or $1400-$17FF)
||         $B: Select 1 KB CHR bank at PPU $0C00-$0FFF (or $1C00-$1FFF)
|+-------- Invert PRG A14
+--------- Invert CHR A12

Power-on values:
* Standard MMC3 Registers $0-$7: $00, $02, $04, $05, $06, $07, $00, $01
* Extended MMC3 Registers $8-$B: $FE, $FF, $FF, $FF

The address mask in the $5000-$5FFF range is determined by the solder pad setting:

Pad setting  Address mask
-----------  ------------
0            $5013
1            $5023
2            $5043
3            $5083
4            $5103
5            $5203
6            $5403
7            $5803

• A solder pad setting of zero (address mask $5013) will produce a usable result for any ROM image.
• Some multicarts only display their menu at settings other than 0.

Later Waixing games (and re-releases of earlier games) use the RAM Configuration Register for copy-protection purposes:

• Write $A1 to $A001: Address range $5000-$5FFF to second half of 8 KiB WRAM bank 2, mapper registers there are disabled.
• Write three values to $5000, $5010 and $5013.
• Do further initialization.
• Write $E2 to $A001. Mapper registers in address range $5000-$5FFF; WRAM at CPU $6000-$7FFF points to 8 KiB WRAM bank 2.
• Copy 20 bytes from $7000 to $6000.
• Copy and XOR bytes from $6000, $6010 and $6013 to $0100-$0102.
• Execute code at CPU $0100.

Hacked ROMs can be detected by them writing to $5000/$5010/$5013 but then no longer jumping to $0100.

• NES 2.0 Mapper 523 is a variant of this mapper with hard-wired mirroring that connects CHR-ROM differently to produce 4/2 KiB instead of 2/1 KiB banks.
• MMC3 with CHR ROM and CHR RAM

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