NES 2.0: Difference between revisions

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'''NES 2.0''' is an extension to the [[iNES]] ROM format, originally [http://forums.nesdev.org/viewtopic.php?p=17727#p17727 proposed] by Kevin Horton on 2006-09-18.
'''NES 2.0''' extends the [[iNES]] single file cart format to better describe NES/Famicom-compatible cartridge hardware. Some of its purpose include:
* Removing the need to use ROM checksums, or other information outside the header, to disambiguate emulation behavior not encoded by iNES.
* Making room for new mapper allocation.
* Allowing for larger ROM sizes.
* Supporting other than standard NES/Famicom console types such as the Nintendo Vs. System and enhanced Famiclones.
* Providing additional information such as the region-specific CPU/PPU type and default expansion port devices.
* Replaces the deprecated [[UNIF]] format.


It adds extra header information to disambiguate ROMs that incompatibly require the same iNES [[mapper]], or supplemental information for ROMs that are otherwise inadequately described by the original format.
The format is [[#Backwards Compatibility to iNES|backwards-compatible]] to iNES, so that ROM images with a NES 2.0 header run in non-NES-2.0-compliant emulators as long as they do not require NES-2.0-exclusive features.


This extension is backwards compatible with the original format, identified by two bits in [[#Byte 7 (Flags 7)|byte 7]] of the header.
=Identification=
A file is a NES 2.0 ROM image file if it begins with "NES<EOF>" (same as iNES) and, additionally, the byte at offset 7 has bit 2 clear and bit 3 set:
bool iNESFormat=false;
if (header[0]=='N' && header[1]=='E' && header[2]=='S' && header[3]==0x1A)
        iNESFormat=true;
bool NES20Format=false;
if (iNESFormat==true && (header[7]&0x0C)==0x08)
        NES20Format=true;
=File Structure=
A NES 2.0 file contains a sixteen-byte header, followed by Trainer, PRG-ROM, CHR-ROM and Miscellaneous ROM data.


== Overview ==
==Header==
Offset Meaning
--------------
0-3    Identification String. Must be "NES<EOF>".
4      [[#PRG-ROM Area|PRG-ROM]] size LSB
5      [[#CHR-ROM Area|CHR-ROM]] size LSB
6      Flags 6
        D~7654 3210
          ---------
          NNNN FTBM
          |||| |||+-- [[#Nametable layout|Hard-wired nametable layout]]
          |||| |||    0: Vertical arrangement ("mirrored horizontally") or mapper-controlled
          |||| |||    1: Horizontal arrangement ("mirrored vertically")
          |||| ||+--- "Battery" and other non-volatile memory
          |||| ||      0: Not present
          |||| ||      1: Present
          |||| |+--- 512-byte [[#Trainer Area|Trainer]]
          |||| |      0: Not present
          |||| |      1: Present between Header and PRG-ROM data
          |||| +---- [[#Nametable layout|Alternative nametables]]
          ||||        0: No
          ||||        1: Yes
          ++++------ Mapper Number D3..D0
7      Flags 7
        D~7654 3210
          ---------
          NNNN 10TT
          |||| ||++- Console type
          |||| ||    0: Nintendo Entertainment System/Family Computer
          |||| ||    1: Nintendo [[Vs. System]]
          |||| ||    2: Nintendo [[PC10 ROM-Images|Playchoice 10]]
          |||| ||    3: [[#Extended Console Type|Extended Console Type]]
          |||| ++--- NES 2.0 identifier
          ++++------ Mapper Number D7..D4
8      [[Mapper]] MSB/[[Submapper]]
        D~7654 3210
          ---------
          SSSS NNNN
          |||| ++++- Mapper number D11..D8
          ++++------ Submapper number
9      [[#PRG-ROM Area|PRG-ROM]]/[[#CHR-ROM Area|CHR-ROM]] size MSB
        D~7654 3210
          ---------
          CCCC PPPP
          |||| ++++- PRG-ROM size MSB
          ++++------ CHR-ROM size MSB
10    [[#PRG-(NV)RAM/EEPROM|PRG-RAM/EEPROM]] size
        D~7654 3210
          ---------
          pppp PPPP
          |||| ++++- PRG-RAM (volatile) shift count
          ++++------ PRG-NVRAM/EEPROM (non-volatile) shift count
        If the shift count is zero, there is no PRG-(NV)RAM.
        If the shift count is non-zero, the actual size is
        "64 << shift count" bytes, i.e. 8192 bytes for a shift count of 7.
11    [[#CHR-(NV)RAM|CHR-RAM]] size
        D~7654 3210
          ---------
          cccc CCCC
          |||| ++++- CHR-RAM size (volatile) shift count
          ++++------ [[:Category:Mappers with battery-backed CHR-RAM|CHR-NVRAM]] size (non-volatile) shift count
        If the shift count is zero, there is no CHR-(NV)RAM.
        If the shift count is non-zero, the actual size is
        "64 << shift count" bytes, i.e. 8192 bytes for a shift count of 7.
12    [[#CPU/PPU Timing|CPU/PPU Timing]]
        D~7654 3210
          ---------
          .... ..VV
                ++- CPU/PPU timing mode
                      0: RP2C02 ("NTSC NES")
                      1: RP2C07 ("Licensed PAL NES")
                      2: Multiple-region
                      3: UA6538 ("Dendy")
13    When Byte 7 AND 3 =1: [[#Vs. System Type|Vs. System Type]]
        D~7654 3210
          ---------
          MMMM PPPP
          |||| ++++- Vs. PPU Type
          ++++------ Vs. Hardware Type
        When Byte 7 AND 3 =3: [[#Extended Console Type|Extended Console Type]]
        D~7654 3210
          ---------
          .... CCCC
              ++++- Extended Console Type
14    [[#Miscellaneous ROM Area|Miscellaneous ROMs]]
        D~7654 3210
          ---------
          .... ..RR
                ++- Number of miscellaneous ROMs present
15    [[#Default Expansion Device|Default Expansion Device]]
        D~7654 3210
          ---------
          ..DD DDDD
            ++-++++- Default Expansion Device


*Written by K.Horton
==Trainer Area==
*Thanks to Quietust for ideas and proofing and help
The Trainer Area follows the 16-byte Header and precedes the PRG-ROM area if bit 2 of Header byte 6 is set. It is always 512 bytes in size if present,
and contains data to be loaded into CPU memory at $7000. It is only used by some games that were modified to run on different hardware from the original cartridges,
such as early RAM cartridges and emulators, and which put some additional compatibility code into those address ranges.
==PRG-ROM Area==
The PRG-ROM Area follows the 16-byte Header and the Trainer Area and precedes the CHR-ROM Area. Header byte 4 (LSB) and bits 0-3 of Header byte 9 (MSB) together specify its size.
If the MSB nibble is $0-E, LSB and MSB together simply specify the PRG-ROM size in 16 KiB units:
  ++++----------- Header byte 9 D3..D0
  |||| ++++-++++- Header byte 4
D~BA98 7654 3210
  --------------
  BBBB BBBB BBBB
  ++++-++++-++++- PRG-ROM size in 16 KiB units,
                  values $000-$EFF for 0..62,898,176 bytes
If the MSB nibble is $F, an exponent-multiplier notation is used:
  ++++----------- Header byte 9 D3..D0
  |||| ++++-++++- Header byte 4
D~BA98 7654 3210
  --------------
  1111 EEEE EEMM
        |||| ||++- Multiplier, actual value is MM*2+1 (1,3,5,7)
        ++++-++--- Exponent (2^E), 0-63
The actual PRG-ROM size is 2^E *(MM*2+1) bytes.
The exponent-multiplier form may only be used if the PRG-ROM size cannot be specified correctly using the simpler notation. If the PRG-ROM data has an odd size that cannot
be represented in either notation, the data must be padded to a size that can be represented.


NES 2.0 is an addition to the standard .NES file format that most emulators use.
In Vs. Dual System ROM images, the first half block of the specified PRG-ROM size belongs to the first unit, and the second half block of PRG-ROM belongs to the the second unit.
It is designed to disambiguate certain ROMs that formerly could have been only be discerned via a CRC-32 or similar hash check.
24 KiB (half-)blocks are mapped to $A000-$FFFF both in Vs. Unisystem and Vs. Dual System.
Naturally, this caused problems for new ROMs that are not in the database but need special handling, such as fan translations, other ROM hacks, and new homebrew on compatible boards.
An exception is granted for two oddly-sized Vs. System ROM images with a total of 40 KiB PRG-ROM, which are defined to represent 32 KiB +8 KiB instead:
* ''Vs. Gumshoe'', [[#Vs. System Type|Vs. Hardware type]] #0:
** First 32 KiB represent the entire CPU $8000-$FFFF area, including the CPU $8000-$9FFF area with $4016 D2=0;
** Second 8 KiB represent the CPU $8000-$9FFF area with $4016 D2=1.
* ''Vs. Raid on Bungeling Bay'', [[#Vs. System Type|Vs. Hardware type]] #6:
** First 32 KiB represent the first unit's PRG-ROM at CPU $8000-$FFFF;
** Second 8 KiB represent the second unit's PRG-ROM at CPU $E000-$FFFF.
** The second unit only executes a dummy program that does nothing except set a flag in the shared WRAM at $6000-$67FF.


There are four goals for this specification:
==CHR-ROM Area==
#Retain 100% backwards compatibility with existing emulators/ROMs/etc. (*this includes "dirty ROMs" with crap such as "DiskDude!" in the header and other atrocities*)
The CHR-ROM Area, if present, follows the Trainer and PRG-ROM Areas and precedes the Miscellaneous ROM Area. Header byte 5 (LSB) and bits 4-7 of Header byte 9 (MSB)
#The format must be "future proof".
specify its size. If the MSB nibble is $0-E, LSB and MSB together simply specify the CHR-ROM size in 8 KiB units:
#The changes made must be very carefully documented and make sense.
  ++++----------- Header byte 9 D7..D4
#Said changes must make sense from both a hardware and software standpoint.
  |||| ++++-++++- Header byte 5
D~BA98 7654 3210
  --------------
  BBBB BBBB BBBB
  ++++-++++-++++- CHR-ROM size in 8 KiB units,
                  values $000-$EFF for 0..31,449,088 bytes
If the MSB nibble is $F, an exponent-multiplier notation is used:
  ++++----------- Header byte 9 D7..D4
  |||| ++++-++++- Header byte 5
D~BA98 7654 3210
  --------------
  1111 EEEE EEMM
        |||| ||++- Multiplier, actual value is MM*2+1 (1,3,5,7)
        ++++-++--- Exponent (2^E), 0-63
The actual CHR-ROM size therefore becomes 2^E * (MM*2+1).
The exponent-multiplier form may only be used if the CHR-ROM size cannot be specified correctly using the simpler notation. If the CHR-ROM data has an odd size that cannot
be represented by either notation, the data must be padded to a size that can be represented.


The name of this specification is "NES 2.0".
For Vs. Dual System ROM images, if the CHR-ROM size is 32 KiB, the first 16 KiB belong to the first unit, and the second 16 KiB of CHR-ROM belong to the second unit.
Do not confuse with "iNES 2.0" which is an emulator that does not support extended features of NES 2.0 headers.
If the CHR-ROM size is 16 KiB, the both units use the same bank-switched 16 KiB CHR-ROM data.


== Existing header ==
==Miscellaneous ROM Area==
The standard specification as popularized by the iNES emulator is presented below:
The Miscellaneous ROM Area, if present, follows the CHR-ROM area and occupies the remainder of the file. Its size is not explicitly denoted in the header, and can be deduced
by subtracting the 16-byte Header, Trainer, PRG-ROM and CHR-ROM Area sizes from the total file size. The meaning of this data depends on the console type and mapper type; Header
byte 14 is used to denote the presence of the Miscellaneous ROM Area and the number of ROM chips in case any disambiguation is needed. Currently, miscellaneous ROMs are defined
for the following situations:
* on console type [[PC10 ROM-Images|Playchoice 10]], an 8 KiB INST ROM, 16 bytes of PROM Data, 16 bytes of PROM Counter Out data, for a total of "3" miscellaneous ROMs;
* on console type [[VT369]], 4 KiB of ROM that is embedded into the NES-on-a-chip itself;
* on [[INES Mapper 086]] submapper 1, a single miscellaneous ROM containing speech data;
* on [[NES 2.0 Mapper 355]], the embedded ROM of the PIC16C54 microcontroller that the games use for protection purposes.
* on [[NES 2.0 Mapper 561]] and [[NES 2.0 Mapper 562]] to deliver trainers that do not match the iNES trainer conventions in size (512 byte) or location ($7000).


<pre>
=Notes=
0-3: string    "NES"<EOF>
==Backwards Compatibility to iNES==
  4: byte      Number of 16384 byte program ROM pages
* Bytes 0-7 have the same meaning as in [[iNES]], so that NES-2.0-headered games will still run in emulators that do not support NES 2.0 unless the header specifies features that those older emulators did not support anyway.
  5: byte      Number of 8192 byte character ROM pages (0 indicates CHR RAM)
* The NES 2.0 identifier (Byte 7 D3..D2) has been chosen so that it does not collide with any valid iNES header nor with any known ROM image that has garbage in bytes 7-15 such as "DiskDude!".
  6: bitfield  Flags 6
==Nametable layout==
  7: bitfield  Flags 7
Byte 6 (Flags 6) contains two bits to describe the [[Mirroring#Nametable Mirroring|nametable layout]] of the cartridge.
8-15: byte      These bytes are not used, and should be 00h.
</pre>


The PRG ROM size is in 16384 byte units, and the CHR ROM size is in 8192 byte units.
  D~7654 3210
If the actual game's data is smaller, such as 8192-byte PRG for Galaxian or 4096-byte CHR for Slappin', double it up and call it a day.
    ---------
For example, if the PRG ROM data is 16384 bytes long, and the first 8192 bytes of the PRG ROM data match the second 8192 bytes, the PRG ROM is an 8Kx8 chip.
    .... F..M
        |  +-- Horizontal/vertical hard-wired mirroring.
        +----- All other nametable layout variations


=== Byte 6 (Flags 6) ===
* Bit 0 is normally relevant only if the mapper does not allow the mirroring type to be switched. It should be set to zero otherwise.
<pre>
* For some mappers, bit 3 means that 4 KiB of RAM are present at PPU $2000-2FFF, exclusive to that region, and cannot be banked, replaced, or rearranged. This applies to:
7      0
** [[INES Mapper 004|Mapper 4]] (MMC3)
---------
** [[INES Mapper 206|Mapper 206]] (DxROM, etc. MMC3-like subset)
NNNN FTBM
** [[NES 2.0 Mapper 262|Mapper 262]] (Street Heroes)
* Several mappers use bit 3 to mean something different:
** [[INES Mapper 030#Nametable Configuration|Mapper 30]] (UNROM 512) - This board can be wired for H/V fixed, 1-screen, or 4-screen.
** [[INES Mapper 218|Mapper 218]] (Magic Floor) - This experimental board has 4 configurations that allow the internal 2k CIRAM to be used for both CHR and nametables at once.


N: Lower 4 bits of the mapper number
==PRG-(NV)RAM/EEPROM==
F: Four screen mode. 0 = no, 1 = yes. (When set, the M bit has no effect)
The PRG-(NV)RAM/EEPROM fields specify the sizes of...
T: Trainer.  0 = no trainer present, 1 = 512 byte trainer at 7000-71FFh
* Memory that is mapped into CPU address space, regardless of whether that memory is internal to a mapper chip or in a separate RAM chip;
B: SRAM at 6000-7FFFh battery backed. 0= no, 1 = yes
* EEPROM even if it is not mapped into CPU address space.
M: Mirroring.  0 = horizontal, 1 = vertical.
They do not specify the sizes of...
</pre>
* Mapper-chip-internal memory that is not mapped into CPU address space, even if battery-backed, such as the [[Namco 163]]'s wavetable RAM which some games use to store saved game data. The size of such memory is part of the Mapper definition instead. The Battery bit (Header byte 6 bit 1) denotes whether such memory is battery-backed. The [[MMC5]]'s EXRAM is not included in the PRG-RAM size, as it can be mapped by software to CPU, PPU, or no address space at all;
None of this changes in NES 2.0.
* self-flashable PRG-ROM;
KH discovered that very few existing ROMs have a trainer, and most of these aren't real trainers at all but subroutines used by a mapper hack.
* external storage such as cassette tape or the ASCII Turbo File.
When the upper nibble (PRG-NVRAM/EEPROM) has a non-zero value, the Battery bit (Header byte 6 bit 1) must always be set for compatibility with [[iNES]]. Conversely, if the Battery bit is set, the upper nibble must have a non-zero value, unless the only battery-backed memory is either mapper-chip-internal memory that is not mapped into CPU address space, such as the [[Namco 163]]'s wavetable RAM, or the PRG-ROM is self-flashable.


=== Byte 7 (Flags 7) ===
==CHR-(NV)RAM==
Later versions of the iNES emulator introduced a second byte of flags.
* In the presence of a NES 2.0 Header, an emulator must not assume that if a ROM image specifies no CHR-ROM, the game will automatically have 8 KiB of CHR-RAM; all CHR-RAM must instead be explicitly specified in Header byte 11.
<pre>
* Memory that is permanently mapped into the nametable address space (PPU $2000-$2FFF) is not included in the CHR-RAM size. Setting the hard-wired four-screen mode bit in Header byte 6 bit 3 therefore does not entail a 4 KiB increase of the CHR-RAM size.
7      0
* The [[MMC5]]'s EXRAM is not included in the CHR-RAM size, as it can be mapped by software to CPU, PPU, or no address space at all.
---------
NNNN xxPV


N: Upper 4 bits of the mapper number
==CPU/PPU Timing==
P: Playchoice 10.  When set, this is a PC-10 game
For non-homebrew NES/Famicom games, this field's value is always a function of the region in which a game was released:
V: Vs. Unisystem. When set, this is a Vs. game
Value  Meaning  Regions
x: these bits are not used in iNES.
  0      RP2C02    North America, Japan, South Korea, Taiwan
</pre>
1      RP2C07    Western Europe, Australia
Early ROM processing tools were not aware of Flags 7 because the earliest emulators ignored it.
2      Multiple  Multiple
For example, one tool put 0x44 (ASCII for 'D', the first character of "DiskDude!") here.
3      UA6538    Eastern Europe, Russia, Mainland China, India, Africa
This confuses newer emulators, which combine the nibbles from Flags 6 and Flags 7 to form an incorrect mapper number.
Value 2 ("multiple-region") is used either if a game was released with identical ROM content in both NTSC and PAL countries, such as Nintendo's early games, or if the game detects the console's timing and adjusts itself. Emulators should implement this value by either switching to a user-specified "Default Region" or by keeping the previously-set region.
NES 2.0 redefines the unused bits to always equal binary 10, which happens not to match any of the patterns used by these ROM processing tools:
<pre>
7      0
---------
NNNN SSPV


N: Upper 4 bits of the mapper number
[[VTxx|V.R. Technology Famiclones]] only come with RP2C02 or UA6538 timing, so games with such a console type can only bear values 0 or 3.
S: When equal to binary 10, use NES 2.0 rules; otherwise, use other rules.
P: Playchoice 10.  When set, this is a PC-10 game
V: Vs. Unisystem. When set, this is a Vs. game
</pre>
That is the "how" of determining whether we are dealing with a valid NES 2.0
file.  Now that that is done, the desired aspects of such a thing need to
be considered.  Kevin has tested over 4000 ROMs and have dumped at least a
thousand more, and reverse engineered probably 60-70 different mappers.
This has given him a front row seat into the shortcomings of the original,
and a good idea of where additional information is needed.


== The problem cases ==
==Vs. System Type==
The new specification needs to clarify five areas:
When the console type in Header byte 7 D1..D0 is 1 (Vs. System), the lower nibble of Header byte 13 specifies the Vs. PPU type, and the upper nibble the non-PPU-based protection
type and whether the ROM is for the Vs. Unisystem or the Vs. Dual System.
Vs. PPU types (Header byte 13 D3..D0):
$0: RP2C03B
$1: RP2C03G
$2: RP2C04-0001
$3: RP2C04-0002
$4: RP2C04-0003
$5: RP2C04-0004
$6: RC2C03B
$7: RC2C03C
$8: RC2C05-01 ($2002 AND $?? =$1B)
$9: RC2C05-02 ($2002 AND $3F =$3D)
$A: RC2C05-03 ($2002 AND $1F =$1C)
$B: RC2C05-04 ($2002 AND $1F =$1B)
$C: RC2C05-05 ($2002 AND $1F =unknown)
$D-F: reserved
For copy protection purposes, these PPU types have different [[PPU palettes|palettes]]; the RC2C05 PPUs furthermore swap [[PPU registers]] $2000 and $2001 and return a signature in the lower bits of $2002. If a game uses the DIP switches to select different PPU models, this field represents the correct PPU model when those DIP switches are all set to zero.
Vs. Hardware type (Header byte 13 D7..D4):
$0: Vs. Unisystem (normal)
$1: Vs. Unisystem (RBI Baseball protection)
$2: Vs. Unisystem (TKO Boxing protection)
$3: Vs. Unisystem (Super Xevious protection)
$4: Vs. Unisystem (Vs. Ice Climber Japan protection)
$5: Vs. Dual System (normal)
$6: Vs. Dual System (Raid on Bungeling Bay protection)
Refer to the [[Vs. System]] entry for more information.
==Extended Console Type==
When the console type in Header byte 7 D1..D0 is 3 (Extended), the lower nibble of Header byte 13 specifies the type of console on which the ROM image is supposed to be run.
$0      [Regular NES/Famicom/Dendy]
$1      [Nintendo Vs. System]
$2      [Playchoice 10]
$3      Regular Famiclone, but with CPU that supports Decimal Mode
$4      Regular NES/Famicom with [[EPSM]] module or plug-through cartridge
$5      [[VT01 STN_Palette|V.R. Technology VT01 with red/cyan STN palette]]
$6      [[VTxx|V.R. Technology VT02]]
$7      [[VTxx|V.R. Technology VT03]]
$8      [[VTxx|V.R. Technology VT09]]
$9      V.R. Technology VT32
$A      V.R. Technology VT369
$B      UMC UM6578
$C      [[Famicom Network System]]
$D-$F  reserved
Values $0-$2 are not used for the extended console type, as they can be expressed by only using Header byte 7 D1..D0. They are reserved here so that emulators
can fold the information in Header Byte 7 D1..D0 and Header byte 13 into one "console type" variable without recoding the values.


=== Vs. Unisystem ===
==Default Expansion Device==
The Vs. Unisystem is one of the two Nintendo arcade machine series produced
Header byte 15 indicates that the ROM expects a specific set of devices accessible at CPU $4016/$4017. For an emulator that wishes to automatically provide selection of needed peripherals, this gives the required information directly within the header.
which use "mostly NES/famicom" hardware.  These games will run fine on
emulators if a little extra things are stored in the header.


Nintendo wanted to make life difficult for arcade operators when it came to
Value $00 is reserved for compatibility with older versions of this specification and indicates no information on the default input device.
copy protection.  Three main schemes were devised. (See the "Vs. system byte"
description below for a detailed analysis)


=== Big ROMs ===
In almost all cases, this byte will specify ''the'' device without which the game cannot be played at all, such as the NES Zapper or Power Pad. If a game supports an ''optional'' expansion port device, and having that device connected does not preclude using the normal controllers with that game, this byte will specify that device, such as the ASCII Turbo File or the Arkanoid Vaus Controller. For games that support multiple combinations of expansion devices, this byte will denote the game's default selection.


PRG ROM has already surpassed 2 MiB, and CHR ROM has already surpassed 1 MiB, especially on pirate multicarts.
This byte does not denote devices that connect to a cartridge; such devices are part of the respective Mapper's definition.
So far, the hack has been to set PRG ROM to 00h to indicate 4Mbytes of ROM (since FFh is 16K short of 4Mbytes).
$00    Unspecified
And in the case of exceeding the 2Mbyte-8K CHR barrier, ROMs have been allocating the CHR in the PRG space.
$01    [[Standard controller|Standard NES/Famicom controllers]]
This can get very messy for an emulator to sort out, especially by 2015 now that pirates are making monstrosities like the CoolBoy ''400 in 1 Real Game'' multicart<ref>SomeRussianMarioDude's [http://somerussianmariodude.blogspot.ru/2014/02/400-in-1-real-game-famicom-review.html review</ref></ref> dumped by TeamEurope, which is 32 MB.<ref>CaH4e3's [http://cah4e3.shedevr.org.ru/dumping_2015.php Dumping 2015]</ref>.
$02    NES [[Four Score]]/Satellite with two additional standard controllers
$03    Famicom Four Players Adapter with two additional standard controllers using the [[Four player adapters#"Simple" Famicom adapters|"simple"]] protocol
$04    [[Vs. System]] (1P via $4016)
$05    Vs. System (1P via $4017)
$06    Reserved
$07    Vs. [[Zapper]]
$08    [[Zapper]] ($4017)
$09    Two Zappers
$0A    Bandai Hyper Shot Lightgun
$0B    [[Power Pad]] Side A
$0C    [[Power Pad]] Side B
$0D    [[Power Pad#Family Trainer Mat|Family Trainer]] Side A
$0E    [[Power Pad#Family Trainer Mat|Family Trainer]] Side B
$0F    [[Arkanoid controller|Arkanoid Vaus Controller (NES)]]
$10    [[Arkanoid controller|Arkanoid Vaus Controller (Famicom)]]
$11    Two Vaus Controllers plus [[Family BASIC Data Recorder|Famicom Data Recorder]]
$12    [[Konami Hyper Shot]] Controller
$13    [[Coconuts Pachinko]] Controller
$14    [[Exciting Boxing Punching Bag]] (Blowup Doll)
$15    [[Jissen Mahjong controller|Jissen Mahjong Controller]]
$16    [[Partytap|Party Tap]]
$17    [[Oeka Kids tablet|Oeka Kids Tablet]]
$18    Sunsoft Barcode Battler
$19    [[Miracle_Piano|Miracle Piano Keyboard]]
$1A    Pokkun Moguraa (Whack-a-Mole Mat and Mallet)
$1B    Top Rider (Inflatable Bicycle)
$1C    Double-Fisted (Requires or allows use of two controllers by one player)
$1D    [[Famicom 3D glasses|Famicom 3D System]]
$1E    Doremikko Keyboard
$1F    R.O.B. Gyro Set
$20    [[Family BASIC Data Recorder|Famicom Data Recorder]] ("silent" keyboard)
$21    ASCII Turbo File
$22    IGS Storage Battle Box
$23    [[Family BASIC Keyboard]] plus Famicom Data Recorder
$24    Dongda PEC-586 Keyboard
$25    Bit Corp. Bit-79 Keyboard
$26    Subor Keyboard
$27    Subor Keyboard plus [[Mouse#Subor Mouse|mouse]] (3x8-bit protocol)
$28    Subor Keyboard plus mouse (24-bit protocol via $4016)
$29    [[Super NES Mouse|SNES Mouse]] ($4017.d0)
$2A    Multicart
$2B    Two [[SNES_controller|SNES controllers]] replacing the two standard NES controllers
$2C    RacerMate Bicycle
$2D    U-Force
$2E    R.O.B. Stack-Up
$2F    City Patrolman Lightgun
$30    Sharp C1 Cassette Interface
$31    Standard Controller with swapped Left-Right/Up-Down/B-A
$32    Excalibur Sudoku Pad
$33    ABL Pinball
$34    Golden Nugget Casino extra buttons
$35    Unknown famiclone keyboard used by the "Golden Key" educational cartridge
$36    Subor Keyboard plus mouse (24-bit protocol via $4017)
$37    [[Port test controller]]
$38    Bandai Multi Game Player Gamepad buttons
$39    Venom TV Dance Mat
$3A    LG TV Remote Control
$3B    [[Famicom Network Controller]]
$3C    King Fishing Controller
$3D    Croaky Karaoke Controller
Notes:
* The Famicom Four Players Adapter ($03) is denoted only if the additional controllers provide ''independent'' 3P/4P input, not if they just alias the built-in 1P/2P controllers.
* So far, there have been no games that provide independent 3P/4P input solely through the [[Four player adapters#Hori 4 Players Adapter|"Hori"]] protocol, which is why there has been no value assigned for it yet.
* For Vs. System games that do not care which stick is used and therefore could be denoted either with value $04 or $05, use value $04.
* Value $06 originally denoted "Pinball (Japan)" and was thought to represent a unique wiring variant, but was since found to represent a peculiar MAME behavior that MAME has since removed.
* "Two Vaus Controllers plus Famicom Data Recorder" ($11) can be trivially emulated as just connecting a Famicom Vaus controller, or sophisticatedly emulated as "Connect two daisy-chained Vaus controllers on startup, disconnect them and connect Family BASIC keyboard with Data Recorder when the user selects Tape Playback or Tape Record from the emulator's user interface; detach these and re-connect the two Vaus controllers when the user selects Tape Stop".
* "Double-Fisted" ($1C) assumes a Four Score is connected, which allows two players to use two controllers at once (Smash T.V.) if the game supports two players.
* The difference between "Famicom Data Recorder" ($20) and "Family BASIC Keyboard" ($23) is that although $20 emulates the Family BASIC keyboard's response to strobe, no actual emulated keyboard input is registered ("silent" keyboard), allowing desktop emulators to keep allowing the use of the host's keyboard for other purposes (such as D-Pad input), and not necessitating the display of an on-screen keyboard on mobile emulators.
* "Multicart" ($2A) is only used if any game on that multicart actually uses expansion port devices. As these will be mostly Zapper games, emulating an expansion port Zapper together with two standard controllers is the simplest way of implementing this value.
* The [[PowerPak]] official loader considers any .NES with a non-zero byte 15 to be invalid, and will fail to load the ROM. A [https://forums.nesdev.org/viewtopic.php?p=283943#p283943 patched N.MAP loader] is available.


=== Submappers ===
==Version History==
See: [[NES 2.0 submappers]]
* 2006-09-18 - Original version of specification by kevtris.
** [https://forums.nesdev.org/viewtopic.php?p=17727#p17727 NES 2.0 "Official" Specification]
* 2019-01-02 - Additions by NewRisingSun.
** [https://forums.nesdev.org/viewtopic.php?f=3&t=17213&start=45#p220624 Additions proposal by NewRisingSun]
** Flags 7: adds [[#Extended Console Type|Extended Console Type]] value
** Flags 12: adds [[#CPU/PPU Timing|Dendy]] value
** Flags 13: adds [[#Extended Console Type|Extended Console Type]] field
** Flags 14: adds [[#Miscellaneous ROM Area|miscellaneous ROM]] specifier
** Flags 15: adds [[#Default Expansion Device|Default Expansion Device]]


Occasionally, two mappers get one number.
==See Also==
Sometimes, an emulator can distinguish them easily: [[iNES Mapper 034|34]] covers both [[NINA-001]] and [[BNROM]], but NINA-001 has CHR ROM, and BNROM has CHR RAM.
* [[NES 2.0 submappers]] - disambiguation for mappers that were under-specified in iNES 1
But other mappers are messier: [[iNES Mapper 083|mapper 83]] (two styles of CHR ROM banking), [[SxROM|mapper 1]] (various ROM/RAM hacks), [[Bandai FCG board|mapper 16]] (EEPROM/WRAM/light pen/etc).
* [[NES 2.0 header for ca65]] - macro header generator for ca65 assembly
* [[NES 2.0 header for cc65]] - macro header generator for cc65 C code


Currently, the only fix for this is to CRC the games and then hack the mapper
==References==
if the CRC or other hash matches.  This of course fails if the game is not
* [https://forums.nesdev.org/viewtopic.php?p=17727#p17727 Original proposal by kevtris]
in the database, especially newly developed homebrew games.
* [https://forums.nesdev.org/viewtopic.php?f=3&t=17213&start=45#p220624 Additions proposal by NewRisingSun]
 
* [https://forums.nesdev.org/viewtopic.php?t=19940 NES 2.0 XML Database, with link to Python script for applying it to a ROM files collection]
=== Mapper number exhaustion ===
 
Face it: we're running out.
In the early days of iNES, 16 mappers seemed like it would be enough, but they were quickly exhausted.
Then 256 mappers seemed like a vast space to work on.
But now, we are getting near the end of the line, and running out of mapper numbers.
Mr. Horton alone has assigned at least 50 or 60 of them, which is almost a quarter of the total mapper space.
 
=== WRAM ===
 
Not all carts that support PRG RAM support 8K of it.
Some support less, some support more, and [[Bandai FCG board|some by Bandai]] even have EEPROM!
Heck, some carts even battery backed the stupid CHR RAM.
This last one was a very recent find at the time NES 2.0 was first written and goes to show that a workable extension needs to reasonably cover all possible bases.
 
== The proposed solution ==
 
=== Byte 8 (Mapper variant) ===
<pre>
7      0
---------
SSSS MMMM
 
S: Submapper number.  Mappers not using submappers set this to zero.
M: Bits 11-8 of mapper number.
</pre>
[[NES 2.0 submappers|Submappers]] are used to disambiguate iNES 1 mappers that require multiple incompatible implementations.
Most mappers will not use submappers; they set S to 0.
 
It's not recommended yet as of 2015 to assign mapper numbers greater than 255.
There were still a couple dozen existing numbers left in [[mapper|the current iNES mapper space]] as of 2013.
Mapper numbers up to 511 should hold us until they stop making ''Ice Age'' films;
mapper numbers up to 4095 should hold us until the next ''literal'' ice age.
 
In 2013, there was a [http://forums.nesdev.org/viewtopic.php?f=3&t=9854 proposal on the BBS] to break up the expanded mapper space into "planes", much like those of [[wikipedia:Plane (Unicode)|Unicode when it expanded past UCS-2]].
Each M value would thus correspond to one plane:
* Plane 0 (0-255): Basic Multilingual Plane, the current mess
* [[Mapper#Plane 1|Plane 1]] (256-511): Mostly for new homebrew mappers.
* [[Mapper#Plane 2|Plane 2]] (512-767): For new dumps of East Asian games.
* Plane 15: Private use area (not for publicly distributed dumps)
 
=== Byte 9 (Upper bits of ROM size) ===
<pre>
7      0
---------
CCCC PPPP
 
C: 4 more CHR ROM size bits
P: 4 more PRG ROM size bits
</pre>
These combine with the existing 8 bits of each to form 12 bits total
for the number of PRG and CHR banks... this is enough for 64Mbytes-16K
of PRG data and 32Mbytes-8K of CHR data.
 
Only a few mappers, mostly multicart mappers, support non-power-of-two sizes for PRG and CHR.
The behavior of a ROM with a Nintendo MMC and a non-power-of-two ROM size is undefined.
 
=== Byte 10 (RAM size) ===
<pre>
7      0
---------
pppp PPPP
 
p: Quantity of PRG RAM which is battery backed (or serial EEPROM, see below)
P: Quantity of PRG RAM which is NOT battery backed
</pre>
The PRG RAM need not be actual RAM; it may also be [[ROM|EEPROM]].
Serial EEPROMs are familiar to developers of Game Boy Advance and Nintendo DS emulators.
But they're older than that:
some [[iNES Mapper 016|mapper 16]] (Bandai) games use serial EEPROMs to store the game data,
rather than a battery backed SRAM.
They most often used the 24C01 (with 128 bytes) or 24C02 (with 256 bytes), but there's no practical limitation on total size. Both ICs use the [[wikipedia:I²C|I²C]] bus.
 
Some games on [[SxROM|SOROM]] or [[ExROM|ETROM]] have two PRG RAM chips, one battery-backed and one not.
Which chip appears earlier in PRG RAM address space depends on the mapper.
For example, SOROM (mapper 1, no CHR ROM, 8192 byte CHR RAM, 8192+8192 byte PRG RAM) puts the battery-backed chip at bank 2 and the other chip at bank 0.
 
Most discrete logic mappers lacked specific support for PRG RAM.
For these mappers, emulators should continue the iNES tradition of extending the stock mappers' functionality in the same way that ''Family BASIC'' extended that of mapper 0.
A cartridge can have up to 8192 bytes of either battery-backed or non-battery-backed RAM at $6000-$7FFF,<ref>possibly a dumb iNES 2.0 header question :-): http://forums.nesdev.org/viewtopic.php?p=77288#p77288</ref> decoded with an [[PRG RAM circuit|74HC20 or 74LS139]].
But some mappers have registers in $6000-$7FFF and do not define a mapping for PRG RAM or serial EEPROM, such as [[INES Mapper 086|Jaleco's JF-13]].
Headers for ROMs using these mappers MUST specify 0 for both PRG RAM sizes.
 
Bytes 10 and 11 of the header define the size of the RAM segments exponentially using 4-bit values:
{| class="tabular"
|-
! value || RAM size in bytes
|-
| 0 || 0
|-
| 1 || 128
|-
| 2 || 256
|-
| 3 || 512
|-
| 4 || 1024
|-
| 5 || 2048
|-
| 6 || 4096
|-
| 7 || 8192
|-
| 8 || 16384
|-
| 9 || 32768
|-
| 10 || 65536
|-
| 11 || 131072
|-
| 12 || 262144
|-
| 13 || 524288
|-
| 14 || 1048576
|-
| 15 || Reserved; do not use
|}
Sizes that are not a power of two, such as the 5120 byte battery-backed RAM of [[iNES Mapper 082|Taito's X1-017]], are rounded up.
 
=== Byte 11 (Video RAM Size) ===
<pre>
7      0
---------
cccc CCCC
 
c: Quantity of CHR RAM which is battery backed (yes it exists! see below)
C: Quantity of CHR RAM which is NOT battery backed
</pre>
 
The majority of games with no CHR ROM will have $07 (8192 bytes, not battery backed) in this byte.
Use of $00 with no CHR ROM implies that the game is wired to map nametable memory in CHR space. The value $00 MUST NOT be used if a mapper isn't defined to allow this.
 
Battery-backed CHR RAM exists. The [http://www.nesmuseum.com/racermate.html RacerMate Challenge II] cartridge has 64K of CHR RAM total:
32K is battery backed, and 32K of it is not.
They store all the stats and such in it.
KH traced out the circuit and couldn't believe it.
It probably simplified the routing or power off protection.
 
For backward compatibility, the battery bit in the original [[iNES]] header (byte 6, bit 1) MUST be true if the upper nibble of byte 10 or 11 is nonzero or false otherwise.
 
=== Byte 12 (TV system) ===
Different TV systems have different [[clock rate]]s, and a game's raster effects and difficulty tuning might expect one or the other.
<pre>
7      0
---------
xxxx xxBP
</pre>
P: 0 indicates NTSC mode; 1 is for PAL mode.
;NTSC mode
:262 lines, NMI on line 241, 3 dots per CPU clock
;PAL mode
:312 lines, NMI on line 241, 3.2 dots per CPU clock
;Dendy PAL mode
:312 lines, NMI on line 291, 3 dots per CPU clock, designed for maximum compatibility with NTSC ROMs, but NES 2.0 does not yet indicate that a game is designed for this mode
 
B: When set, indicates this ROM works on both PAL and NTSC machines.
Some of the Codemasters games actually will adjust the game depending on if it [[Detect TV system|detects you running on a PAL or NTSC machine]] - it adjusts the timing of the game and transposes the music.
Not many games would have this B flag set; those that do would be labeled (UE) or the like in GoodNES.
 
=== Byte 13 (Vs. hardware) ===
<pre>
7      0
---------
MMMM PPPP
 
This byte is reserved for the Vs. system only.  If this is not
a Vs. system ROM, the value of this byte must be $00, which
signifies RP2C03B (used in PlayChoice, Famicom Titler, and a
few TVs with built-in Famicom) and no Vs.-specific submapper.
 
P: PPU.  There are 13 Vs. PPUs that can be found on the games:
 
0 - RP2C03B    (bog standard RGB palette)
1 - RP2C03G    (similar pallete to above, might have 1 changed colour)
2 - RP2C04-0001 (scrambled palette + new colours)
3 - RP2C04-0002 (same as above, different scrambling)
4 - RP2C04-0003 (similar to above)
5 - RP2C04-0004 (similar to above)
6 - RC2C03B    (bog standard palette, seems identical to RP2C03B)
7 - RC2C03C    (similar to above, but with 1 changed colour or so)
8 - RC2C05-01  (all five of these have the normal palette...
9 - RC2C05-02  (...but with different bits returned on 2002)
10 - RC2C05-03
11 - RC2C05-04
12 - RC2C05-05
13 - not defined (do not use these)
14 - not defined
15 - not defined
 
KH has a good cross-section of Vs. games and has dumped bit-for-bit
palettes from all thirteen of these PPUs.  The last 5 PPUs (RC2C05)
have the standard NES palette in them, however they return a specific
word in the lower 5 bits of PPUSTATUS ($2002), and the PPUCTRL ($2000)
and PPUMASK ($2001) ports are flipped around (PPUMASK at $2000 and
PPUCTRL at $2001).
 
Nocash and MESS report:
RC2C05-01 (with ID ([2002h] AND ??h)=1Bh)
RC2C05-02 (with ID ([2002h] AND 3Fh)=3Dh)
RC2C05-03 (with ID ([2002h] AND 1Fh)=1Ch)
RC2C05-04 (with ID ([2002h] AND 1Fh)=1Bh)
and cannot find the 2C05-05
 
 
M: Vs. mode:
 
0 - Normal- no special mode(s)
1 - RBI Baseball  (protection hardware at port 5E0xh)
2 - TKO Boxing    (other protection hardware at port 5E0xh)
3 - Super Xevious (protection hardware at port 5xxxh)
4 - ...
</pre>
 
Nintendo did a few things to make piracy difficult for arcade operators:
;Different PPUs: There are 13 different PPU chips found on Vs. arcade boards.
;Different controller pinouts: Some games came with new control panels you had to install with the game.  This was pretty basic stuff and just remapped a few of the buttons. (FIXME: which games do use what special control panels?)
 
=== Byte 14 and 15 (Reserved) ===
Reserved, these two bytes must be zero.
 
== Emulator support ==
*BizHawk as of r6313
*FCEUX as of r3071
*[[Nintendulator]] 0.975 Beta
*MESS (per [http://forums.nesdev.org/viewtopic.php?p=62428#p62428 BBS post 62428])
*no$nes v1.1
*[https://kkfos.aspekt.fi/ PowerMappers] v23 for PowerPak
 
== References ==
<references/>
<references/>
[[Category:File formats]]
[[Category:File formats]]

Revision as of 08:31, 23 March 2024

NES 2.0 extends the iNES single file cart format to better describe NES/Famicom-compatible cartridge hardware. Some of its purpose include:

  • Removing the need to use ROM checksums, or other information outside the header, to disambiguate emulation behavior not encoded by iNES.
  • Making room for new mapper allocation.
  • Allowing for larger ROM sizes.
  • Supporting other than standard NES/Famicom console types such as the Nintendo Vs. System and enhanced Famiclones.
  • Providing additional information such as the region-specific CPU/PPU type and default expansion port devices.
  • Replaces the deprecated UNIF format.

The format is backwards-compatible to iNES, so that ROM images with a NES 2.0 header run in non-NES-2.0-compliant emulators as long as they do not require NES-2.0-exclusive features.

Identification

A file is a NES 2.0 ROM image file if it begins with "NES<EOF>" (same as iNES) and, additionally, the byte at offset 7 has bit 2 clear and bit 3 set:

bool iNESFormat=false;
if (header[0]=='N' && header[1]=='E' && header[2]=='S' && header[3]==0x1A)
        iNESFormat=true;

bool NES20Format=false;
if (iNESFormat==true && (header[7]&0x0C)==0x08)
        NES20Format=true;

File Structure

A NES 2.0 file contains a sixteen-byte header, followed by Trainer, PRG-ROM, CHR-ROM and Miscellaneous ROM data.

Header

Offset Meaning
--------------
0-3    Identification String. Must be "NES<EOF>".

4      PRG-ROM size LSB
5      CHR-ROM size LSB

6      Flags 6
       D~7654 3210
         ---------
         NNNN FTBM
         |||| |||+-- Hard-wired nametable layout
         |||| |||     0: Vertical arrangement ("mirrored horizontally") or mapper-controlled
         |||| |||     1: Horizontal arrangement ("mirrored vertically")
         |||| ||+--- "Battery" and other non-volatile memory
         |||| ||      0: Not present
         |||| ||      1: Present
         |||| |+--- 512-byte Trainer
         |||| |      0: Not present
         |||| |      1: Present between Header and PRG-ROM data
         |||| +---- Alternative nametables
         ||||        0: No
         ||||        1: Yes
         ++++------ Mapper Number D3..D0

7      Flags 7
       D~7654 3210
         ---------
         NNNN 10TT
         |||| ||++- Console type
         |||| ||     0: Nintendo Entertainment System/Family Computer
         |||| ||     1: Nintendo Vs. System
         |||| ||     2: Nintendo Playchoice 10
         |||| ||     3: Extended Console Type
         |||| ++--- NES 2.0 identifier
         ++++------ Mapper Number D7..D4

8      Mapper MSB/Submapper
       D~7654 3210
         ---------
         SSSS NNNN
         |||| ++++- Mapper number D11..D8
         ++++------ Submapper number

9      PRG-ROM/CHR-ROM size MSB
       D~7654 3210
         ---------
         CCCC PPPP
         |||| ++++- PRG-ROM size MSB
         ++++------ CHR-ROM size MSB

10     PRG-RAM/EEPROM size
       D~7654 3210
         ---------
         pppp PPPP
         |||| ++++- PRG-RAM (volatile) shift count
         ++++------ PRG-NVRAM/EEPROM (non-volatile) shift count
       If the shift count is zero, there is no PRG-(NV)RAM.
       If the shift count is non-zero, the actual size is
       "64 << shift count" bytes, i.e. 8192 bytes for a shift count of 7.

11     CHR-RAM size
       D~7654 3210
         ---------
         cccc CCCC
         |||| ++++- CHR-RAM size (volatile) shift count
         ++++------ CHR-NVRAM size (non-volatile) shift count
       If the shift count is zero, there is no CHR-(NV)RAM.
       If the shift count is non-zero, the actual size is
       "64 << shift count" bytes, i.e. 8192 bytes for a shift count of 7.

12     CPU/PPU Timing
       D~7654 3210
         ---------
         .... ..VV
                ++- CPU/PPU timing mode
                     0: RP2C02 ("NTSC NES")
                     1: RP2C07 ("Licensed PAL NES")
                     2: Multiple-region
                     3: UA6538 ("Dendy")

13     When Byte 7 AND 3 =1: Vs. System Type
       D~7654 3210
         ---------
         MMMM PPPP
         |||| ++++- Vs. PPU Type
         ++++------ Vs. Hardware Type

       When Byte 7 AND 3 =3: Extended Console Type
       D~7654 3210
         ---------
         .... CCCC
              ++++- Extended Console Type

14     Miscellaneous ROMs
       D~7654 3210
         ---------
         .... ..RR
                ++- Number of miscellaneous ROMs present

15     Default Expansion Device
       D~7654 3210
         ---------
         ..DD DDDD
           ++-++++- Default Expansion Device

Trainer Area

The Trainer Area follows the 16-byte Header and precedes the PRG-ROM area if bit 2 of Header byte 6 is set. It is always 512 bytes in size if present, and contains data to be loaded into CPU memory at $7000. It is only used by some games that were modified to run on different hardware from the original cartridges, such as early RAM cartridges and emulators, and which put some additional compatibility code into those address ranges.

PRG-ROM Area

The PRG-ROM Area follows the 16-byte Header and the Trainer Area and precedes the CHR-ROM Area. Header byte 4 (LSB) and bits 0-3 of Header byte 9 (MSB) together specify its size. If the MSB nibble is $0-E, LSB and MSB together simply specify the PRG-ROM size in 16 KiB units:

  ++++----------- Header byte 9 D3..D0
  |||| ++++-++++- Header byte 4
D~BA98 7654 3210
  --------------
  BBBB BBBB BBBB
  ++++-++++-++++- PRG-ROM size in 16 KiB units,
                  values $000-$EFF for 0..62,898,176 bytes

If the MSB nibble is $F, an exponent-multiplier notation is used:

  ++++----------- Header byte 9 D3..D0
  |||| ++++-++++- Header byte 4
D~BA98 7654 3210
  --------------
  1111 EEEE EEMM
       |||| ||++- Multiplier, actual value is MM*2+1 (1,3,5,7)
       ++++-++--- Exponent (2^E), 0-63

The actual PRG-ROM size is 2^E *(MM*2+1) bytes.

The exponent-multiplier form may only be used if the PRG-ROM size cannot be specified correctly using the simpler notation. If the PRG-ROM data has an odd size that cannot be represented in either notation, the data must be padded to a size that can be represented.

In Vs. Dual System ROM images, the first half block of the specified PRG-ROM size belongs to the first unit, and the second half block of PRG-ROM belongs to the the second unit. 24 KiB (half-)blocks are mapped to $A000-$FFFF both in Vs. Unisystem and Vs. Dual System. An exception is granted for two oddly-sized Vs. System ROM images with a total of 40 KiB PRG-ROM, which are defined to represent 32 KiB +8 KiB instead:

  • Vs. Gumshoe, Vs. Hardware type #0:
    • First 32 KiB represent the entire CPU $8000-$FFFF area, including the CPU $8000-$9FFF area with $4016 D2=0;
    • Second 8 KiB represent the CPU $8000-$9FFF area with $4016 D2=1.
  • Vs. Raid on Bungeling Bay, Vs. Hardware type #6:
    • First 32 KiB represent the first unit's PRG-ROM at CPU $8000-$FFFF;
    • Second 8 KiB represent the second unit's PRG-ROM at CPU $E000-$FFFF.
    • The second unit only executes a dummy program that does nothing except set a flag in the shared WRAM at $6000-$67FF.

CHR-ROM Area

The CHR-ROM Area, if present, follows the Trainer and PRG-ROM Areas and precedes the Miscellaneous ROM Area. Header byte 5 (LSB) and bits 4-7 of Header byte 9 (MSB) specify its size. If the MSB nibble is $0-E, LSB and MSB together simply specify the CHR-ROM size in 8 KiB units:

  ++++----------- Header byte 9 D7..D4
  |||| ++++-++++- Header byte 5
D~BA98 7654 3210
  --------------
  BBBB BBBB BBBB
  ++++-++++-++++- CHR-ROM size in 8 KiB units,
                  values $000-$EFF for 0..31,449,088 bytes

If the MSB nibble is $F, an exponent-multiplier notation is used:

  ++++----------- Header byte 9 D7..D4
  |||| ++++-++++- Header byte 5
D~BA98 7654 3210
  --------------
  1111 EEEE EEMM
       |||| ||++- Multiplier, actual value is MM*2+1 (1,3,5,7)
       ++++-++--- Exponent (2^E), 0-63

The actual CHR-ROM size therefore becomes 2^E * (MM*2+1).

The exponent-multiplier form may only be used if the CHR-ROM size cannot be specified correctly using the simpler notation. If the CHR-ROM data has an odd size that cannot be represented by either notation, the data must be padded to a size that can be represented.

For Vs. Dual System ROM images, if the CHR-ROM size is 32 KiB, the first 16 KiB belong to the first unit, and the second 16 KiB of CHR-ROM belong to the second unit. If the CHR-ROM size is 16 KiB, the both units use the same bank-switched 16 KiB CHR-ROM data.

Miscellaneous ROM Area

The Miscellaneous ROM Area, if present, follows the CHR-ROM area and occupies the remainder of the file. Its size is not explicitly denoted in the header, and can be deduced by subtracting the 16-byte Header, Trainer, PRG-ROM and CHR-ROM Area sizes from the total file size. The meaning of this data depends on the console type and mapper type; Header byte 14 is used to denote the presence of the Miscellaneous ROM Area and the number of ROM chips in case any disambiguation is needed. Currently, miscellaneous ROMs are defined for the following situations:

  • on console type Playchoice 10, an 8 KiB INST ROM, 16 bytes of PROM Data, 16 bytes of PROM Counter Out data, for a total of "3" miscellaneous ROMs;
  • on console type VT369, 4 KiB of ROM that is embedded into the NES-on-a-chip itself;
  • on INES Mapper 086 submapper 1, a single miscellaneous ROM containing speech data;
  • on NES 2.0 Mapper 355, the embedded ROM of the PIC16C54 microcontroller that the games use for protection purposes.
  • on NES 2.0 Mapper 561 and NES 2.0 Mapper 562 to deliver trainers that do not match the iNES trainer conventions in size (512 byte) or location ($7000).

Notes

Backwards Compatibility to iNES

  • Bytes 0-7 have the same meaning as in iNES, so that NES-2.0-headered games will still run in emulators that do not support NES 2.0 unless the header specifies features that those older emulators did not support anyway.
  • The NES 2.0 identifier (Byte 7 D3..D2) has been chosen so that it does not collide with any valid iNES header nor with any known ROM image that has garbage in bytes 7-15 such as "DiskDude!".

Nametable layout

Byte 6 (Flags 6) contains two bits to describe the nametable layout of the cartridge.

 D~7654 3210
   ---------
   .... F..M
        |  +-- Horizontal/vertical hard-wired mirroring.
        +----- All other nametable layout variations
  • Bit 0 is normally relevant only if the mapper does not allow the mirroring type to be switched. It should be set to zero otherwise.
  • For some mappers, bit 3 means that 4 KiB of RAM are present at PPU $2000-2FFF, exclusive to that region, and cannot be banked, replaced, or rearranged. This applies to:
  • Several mappers use bit 3 to mean something different:
    • Mapper 30 (UNROM 512) - This board can be wired for H/V fixed, 1-screen, or 4-screen.
    • Mapper 218 (Magic Floor) - This experimental board has 4 configurations that allow the internal 2k CIRAM to be used for both CHR and nametables at once.

PRG-(NV)RAM/EEPROM

The PRG-(NV)RAM/EEPROM fields specify the sizes of...

  • Memory that is mapped into CPU address space, regardless of whether that memory is internal to a mapper chip or in a separate RAM chip;
  • EEPROM even if it is not mapped into CPU address space.

They do not specify the sizes of...

  • Mapper-chip-internal memory that is not mapped into CPU address space, even if battery-backed, such as the Namco 163's wavetable RAM which some games use to store saved game data. The size of such memory is part of the Mapper definition instead. The Battery bit (Header byte 6 bit 1) denotes whether such memory is battery-backed. The MMC5's EXRAM is not included in the PRG-RAM size, as it can be mapped by software to CPU, PPU, or no address space at all;
  • self-flashable PRG-ROM;
  • external storage such as cassette tape or the ASCII Turbo File.

When the upper nibble (PRG-NVRAM/EEPROM) has a non-zero value, the Battery bit (Header byte 6 bit 1) must always be set for compatibility with iNES. Conversely, if the Battery bit is set, the upper nibble must have a non-zero value, unless the only battery-backed memory is either mapper-chip-internal memory that is not mapped into CPU address space, such as the Namco 163's wavetable RAM, or the PRG-ROM is self-flashable.

CHR-(NV)RAM

  • In the presence of a NES 2.0 Header, an emulator must not assume that if a ROM image specifies no CHR-ROM, the game will automatically have 8 KiB of CHR-RAM; all CHR-RAM must instead be explicitly specified in Header byte 11.
  • Memory that is permanently mapped into the nametable address space (PPU $2000-$2FFF) is not included in the CHR-RAM size. Setting the hard-wired four-screen mode bit in Header byte 6 bit 3 therefore does not entail a 4 KiB increase of the CHR-RAM size.
  • The MMC5's EXRAM is not included in the CHR-RAM size, as it can be mapped by software to CPU, PPU, or no address space at all.

CPU/PPU Timing

For non-homebrew NES/Famicom games, this field's value is always a function of the region in which a game was released:

Value  Meaning   Regions
0      RP2C02    North America, Japan, South Korea, Taiwan
1      RP2C07    Western Europe, Australia
2      Multiple  Multiple
3      UA6538    Eastern Europe, Russia, Mainland China, India, Africa

Value 2 ("multiple-region") is used either if a game was released with identical ROM content in both NTSC and PAL countries, such as Nintendo's early games, or if the game detects the console's timing and adjusts itself. Emulators should implement this value by either switching to a user-specified "Default Region" or by keeping the previously-set region.

V.R. Technology Famiclones only come with RP2C02 or UA6538 timing, so games with such a console type can only bear values 0 or 3.

Vs. System Type

When the console type in Header byte 7 D1..D0 is 1 (Vs. System), the lower nibble of Header byte 13 specifies the Vs. PPU type, and the upper nibble the non-PPU-based protection type and whether the ROM is for the Vs. Unisystem or the Vs. Dual System.

Vs. PPU types (Header byte 13 D3..D0):
$0: RP2C03B
$1: RP2C03G
$2: RP2C04-0001
$3: RP2C04-0002
$4: RP2C04-0003
$5: RP2C04-0004
$6: RC2C03B
$7: RC2C03C
$8: RC2C05-01 ($2002 AND $?? =$1B)
$9: RC2C05-02 ($2002 AND $3F =$3D)
$A: RC2C05-03 ($2002 AND $1F =$1C)
$B: RC2C05-04 ($2002 AND $1F =$1B)
$C: RC2C05-05 ($2002 AND $1F =unknown)
$D-F: reserved

For copy protection purposes, these PPU types have different palettes; the RC2C05 PPUs furthermore swap PPU registers $2000 and $2001 and return a signature in the lower bits of $2002. If a game uses the DIP switches to select different PPU models, this field represents the correct PPU model when those DIP switches are all set to zero.

Vs. Hardware type (Header byte 13 D7..D4):
$0: Vs. Unisystem (normal)
$1: Vs. Unisystem (RBI Baseball protection)
$2: Vs. Unisystem (TKO Boxing protection)
$3: Vs. Unisystem (Super Xevious protection)
$4: Vs. Unisystem (Vs. Ice Climber Japan protection)
$5: Vs. Dual System (normal)
$6: Vs. Dual System (Raid on Bungeling Bay protection)

Refer to the Vs. System entry for more information.

Extended Console Type

When the console type in Header byte 7 D1..D0 is 3 (Extended), the lower nibble of Header byte 13 specifies the type of console on which the ROM image is supposed to be run.

$0      [Regular NES/Famicom/Dendy]
$1      [Nintendo Vs. System]
$2      [Playchoice 10]
$3      Regular Famiclone, but with CPU that supports Decimal Mode
$4      Regular NES/Famicom with EPSM module or plug-through cartridge
$5      V.R. Technology VT01 with red/cyan STN palette
$6      V.R. Technology VT02
$7      V.R. Technology VT03
$8      V.R. Technology VT09
$9      V.R. Technology VT32
$A      V.R. Technology VT369
$B      UMC UM6578
$C      Famicom Network System
$D-$F   reserved

Values $0-$2 are not used for the extended console type, as they can be expressed by only using Header byte 7 D1..D0. They are reserved here so that emulators can fold the information in Header Byte 7 D1..D0 and Header byte 13 into one "console type" variable without recoding the values.

Default Expansion Device

Header byte 15 indicates that the ROM expects a specific set of devices accessible at CPU $4016/$4017. For an emulator that wishes to automatically provide selection of needed peripherals, this gives the required information directly within the header.

Value $00 is reserved for compatibility with older versions of this specification and indicates no information on the default input device.

In almost all cases, this byte will specify the device without which the game cannot be played at all, such as the NES Zapper or Power Pad. If a game supports an optional expansion port device, and having that device connected does not preclude using the normal controllers with that game, this byte will specify that device, such as the ASCII Turbo File or the Arkanoid Vaus Controller. For games that support multiple combinations of expansion devices, this byte will denote the game's default selection.

This byte does not denote devices that connect to a cartridge; such devices are part of the respective Mapper's definition.

$00     Unspecified
$01     Standard NES/Famicom controllers
$02     NES Four Score/Satellite with two additional standard controllers
$03     Famicom Four Players Adapter with two additional standard controllers using the "simple" protocol
$04     Vs. System (1P via $4016)
$05     Vs. System (1P via $4017)
$06     Reserved
$07     Vs. Zapper
$08     Zapper ($4017)
$09     Two Zappers
$0A     Bandai Hyper Shot Lightgun
$0B     Power Pad Side A
$0C     Power Pad Side B
$0D     Family Trainer Side A
$0E     Family Trainer Side B
$0F     Arkanoid Vaus Controller (NES)
$10     Arkanoid Vaus Controller (Famicom)
$11     Two Vaus Controllers plus Famicom Data Recorder
$12     Konami Hyper Shot Controller
$13     Coconuts Pachinko Controller
$14     Exciting Boxing Punching Bag (Blowup Doll)
$15     Jissen Mahjong Controller
$16     Party Tap 
$17     Oeka Kids Tablet
$18     Sunsoft Barcode Battler
$19     Miracle Piano Keyboard
$1A     Pokkun Moguraa (Whack-a-Mole Mat and Mallet)
$1B     Top Rider (Inflatable Bicycle)
$1C     Double-Fisted (Requires or allows use of two controllers by one player)
$1D     Famicom 3D System
$1E     Doremikko Keyboard
$1F     R.O.B. Gyro Set
$20     Famicom Data Recorder ("silent" keyboard)
$21     ASCII Turbo File
$22     IGS Storage Battle Box
$23     Family BASIC Keyboard plus Famicom Data Recorder
$24     Dongda PEC-586 Keyboard
$25     Bit Corp. Bit-79 Keyboard
$26     Subor Keyboard
$27     Subor Keyboard plus mouse (3x8-bit protocol)
$28     Subor Keyboard plus mouse (24-bit protocol via $4016)
$29     SNES Mouse ($4017.d0)
$2A     Multicart
$2B     Two SNES controllers replacing the two standard NES controllers
$2C     RacerMate Bicycle
$2D     U-Force
$2E     R.O.B. Stack-Up
$2F     City Patrolman Lightgun
$30     Sharp C1 Cassette Interface
$31     Standard Controller with swapped Left-Right/Up-Down/B-A
$32     Excalibur Sudoku Pad
$33     ABL Pinball
$34     Golden Nugget Casino extra buttons
$35     Unknown famiclone keyboard used by the "Golden Key" educational cartridge
$36     Subor Keyboard plus mouse (24-bit protocol via $4017)
$37     Port test controller
$38     Bandai Multi Game Player Gamepad buttons
$39     Venom TV Dance Mat
$3A     LG TV Remote Control
$3B     Famicom Network Controller
$3C     King Fishing Controller
$3D     Croaky Karaoke Controller

Notes:

  • The Famicom Four Players Adapter ($03) is denoted only if the additional controllers provide independent 3P/4P input, not if they just alias the built-in 1P/2P controllers.
  • So far, there have been no games that provide independent 3P/4P input solely through the "Hori" protocol, which is why there has been no value assigned for it yet.
  • For Vs. System games that do not care which stick is used and therefore could be denoted either with value $04 or $05, use value $04.
  • Value $06 originally denoted "Pinball (Japan)" and was thought to represent a unique wiring variant, but was since found to represent a peculiar MAME behavior that MAME has since removed.
  • "Two Vaus Controllers plus Famicom Data Recorder" ($11) can be trivially emulated as just connecting a Famicom Vaus controller, or sophisticatedly emulated as "Connect two daisy-chained Vaus controllers on startup, disconnect them and connect Family BASIC keyboard with Data Recorder when the user selects Tape Playback or Tape Record from the emulator's user interface; detach these and re-connect the two Vaus controllers when the user selects Tape Stop".
  • "Double-Fisted" ($1C) assumes a Four Score is connected, which allows two players to use two controllers at once (Smash T.V.) if the game supports two players.
  • The difference between "Famicom Data Recorder" ($20) and "Family BASIC Keyboard" ($23) is that although $20 emulates the Family BASIC keyboard's response to strobe, no actual emulated keyboard input is registered ("silent" keyboard), allowing desktop emulators to keep allowing the use of the host's keyboard for other purposes (such as D-Pad input), and not necessitating the display of an on-screen keyboard on mobile emulators.
  • "Multicart" ($2A) is only used if any game on that multicart actually uses expansion port devices. As these will be mostly Zapper games, emulating an expansion port Zapper together with two standard controllers is the simplest way of implementing this value.
  • The PowerPak official loader considers any .NES with a non-zero byte 15 to be invalid, and will fail to load the ROM. A patched N.MAP loader is available.

Version History

See Also

References