NES 2.0 submappers: Difference between revisions

Revision as of 16:38, 7 August 2015

Submapper is a term used in the NES 2.0 header for 4-bit codes designating functionally distinct variants of iNES mappers that cannot be distinguished by the memory size fields alone. Most emulators using iNES format distinguish these using CRC, SHA-1, or other hashes of the PRG ROM and CHR ROM, but this works only for games published prior to 1997, not for fan translations or ROM hacks, and not for new games on the same mapper.

Submapper 0 represents the default iNES behavour, so that backward compatibility is maintained.

This document is a living specification. Proposals for new submappers should be made at: Proposals.

001: MMC1

Most MMC1 boards wire all PRG ROM address lines A14-A18 to the mapper's output in a fairly predictable manner.

Boards with CHR RAM wire PRG ROM A18 and the PRG RAM address lines to otherwise unused CHR bank outputs.

Boards designed to take a 32 KiB PRG ROM, either connect PRG ROM A14 to the MMC1's output (SIROM), or directly to CPU A14 (SEROM, SHROM, SH1ROM).

TO DO: which of these games are actually incompatible with the default mapper? Are all of these traditionally CRC cases?

001: 0

Normal behavior. The PRG ROM size and PRG RAM size determine the function of bits.

001: 1

SUROM. (Can also be identified by PRG ROM and PRG RAM size.)

Dragon Warrior III
Dragon Warrior IV / Dragon Quest IV
Ninjara Hoi!'

001: 2

SOROM. (Can also be identified by PRG ROM and PRG RAM size.)

Genghis Khan / Aoki Ookami to Shiroki Mejika: Genghis Khan
Nobunaga's Ambition / Nobunaga no Yabou: Zenkokuban
Romance of the Three Kingdoms
Sangokushi

001: 3

Deprecated. Use iNES Mapper 155 instead.

001: 4

SSROM. (Can also be identified by PRG ROM and PRG RAM size.)

001: 5

SEROM, SHROM, SH1ROM style: PRG ROM A14 connected directly to CPU A14 (and MMC1 A14 input) instead of MMC1 A14 output. Ignore MMC1 A14, ignore LSB of PRG bank, weird behavior of switchable PRG bank if PRG > 32KiB.

Many games: SEROM, SHROM, SH1ROM

032: Irem G101

Major League requires hardwired one-screen mirroring and entirely ignores writes to $9000.

032: 0

Normal (H/V mapper-controlled mirroring)

032: 1

CIRAM A10 is tied high (fixed one-screen mirroring) and PRG banking style is fixed as 8+8+16F

Major League

034: iNES Mapper 034

This iNES mapper unfortunately combines the unrelated BNROM and NINA-001 mappers.

034: 0

Normal. Both mappers can be implemented simultaneously without incompatibility.

Because the NINA-001 supports CHR banking and BNROM does not, the presence of more than 8 KiB of CHR implies NINA-001, and could be used to select between two exclusive mapper implementations.

034: 1

NINA-001 only.

(no extant games require this)

068: Sunsoft 4

In addition to its normal function, the Sunsoft 4 IC was used in Nantettatte!! Baseball which requires different PRG behavior:

068: 0

0: Normal (max 256KiB PRG)

068: 1

1: Sunsoft Dual Cartridge System a.k.a. NTB-ROM (max 128KiB PRG, licensing IC present, external option ROM of up to 128KiB should be selectable by a second menu)

Nantettatte!! Baseball

071

Some games use this with 1-screen mirroring, where the mapper's mirroring control bit is wired directly to CIRAM A10. Others have hardwired horizontal or vertical mirroring.

Another variation of this mapper was used in the Quattro multicarts, but these have been reassigned to mapper 232.

071: 0

Hardwired horizontal or vertical mirroring.

071 : 1

Mapper controlled single-screen mirroring.

Fire Hawk

iNES Mapper 078

One game uses this with 1-screen mirroring, where the mapper's mirroring control bit is wired directly to CIRAM A10. The other can switch between horizontal and vertical mirroring, using a multiplexer between PPU A10 and PPU A11 whose output is sent to CIRAM A10.

0: Not specified
1: Single-screen mirroring (nibble-swapped mapper 152)
2: Ignore mapper output and use fixed V/H/4 mirroring (effectively nibble-swapped mapper 70; not used in commercial games; deprecated)
3: Mapper-controlled H/V mirroring

Source: KH's submappers

iNES Mapper 185

Status: Draft

A few NROM-like games were released on CNROM boards where all four bits of the latch were solely used as an anti-piracy measure. While a documented heuristic exists for which values were used, we tentatively suggest that the submapper here indicate the value to be written to the latch for normal operation (submapper = (latch&0x30)/4+(latch&3))

3210  
||||
|||+- Bit 0 (bank number)
||+-- Bit 1 (bank number)
|+--- Bit 4 (diode config)
+---- Bit 5 (diode config)

In the case that any of the bits are "don't care", use 0.

210: Namco 175 and 340

Status: Draft

Mapper 210 doesn't distinguish between the 175's hardwired mirroring and 340's 1/H/V mirroring. Also, previous confusion and compatibility code used by Namco when they were developing games means that many 175- and 340- using games are incorrectly tagged as mapper 19.

Tentative suggestion:
Mapper 210:
0: No advisory statement is made (use runtime heuristics)
1: N175 (hardwired mirroring, no IRQ)
2: N340 (1/H/V mirroring, no IRQ, no internal or external RAM)