INES Mapper 005
From NESdev Wiki
Jump to navigationJump to search
iNES Mapper 005 refers to ExROM boards, which use the MMC5 mapper.
Many ExROM games have more than one 8 KB page of PRG RAM. Byte 8 of the file's header should indicate how many pages are present, but ROM images in the wild that use this mapper may not have byte 8 set correctly.
Here are Disch's original notes:
========================
= Mapper 005 =
========================
aka
--------------------------
MMC5
ExROM
Example Games:
--------------------------
Castlevania 3
Just Breed
Uncharted Waters
Romance of the 3 Kingdoms 2
Laser Invasion
Metal Slader Glory
Uchuu Keibitai SDF
Shin 4 Nin Uchi Mahjong - Yakuman Tengoku
Test ROM Notes:
---------------------------
- Uchuu Keibitai SDF is the only known game to use split screen mode (during the intro, where it shows ship
stats)
- Shin 4 Nin Uchi Mahjong uses the extra PCM channel ($5011) as well as the other extra sound
- Uncharted Waters does PRG-RAM swapping
- Just Breed uses ExAttribute mode everywhere, as well as the extra sound.
General Notes:
---------------------------
MMC5 is the infamous juggernaut mapper. It does a whole slew of neat tricks, making it far more powerful
than any other mapper around. Though despite it's apparent complexity, it's suprisingly straightforward to
emulate (that doesn't mean it's easy, though).
It's a shame that the only real games to use this mapper were a ton of really, really terrible Koei strategy
games. Such a waste.
RAM Notes:
----------------------------
MMC5 can address up to 64k PRG-RAM! This is significantly more than the usual 8k. When emulating, it's
easiest just to give MMC5 games a full 64k, since the header doesn't really provide a decent way to indicate
how much PRG-RAM actually exists.
In addition to PRG-RAM, the MMC5 itself has a full 1k of 'ExRAM' which can be accessed by both the CPU and
PPU. This ExRAM can be used for many things... from plain vanilla WRAM, to an extra nametable, to a seperate
split screen, to extending normal attribute tables.
This document's organization:
---------------------------
Since there are so many registers for this mapper, and it has so many features, registers will be listed and
outlined as the features are explained... and the overall registers section will be extremely brief --
serving primarily as a very quick reference or checklist.
Misc Modes and Setup:
---------------------------
$5102: [.... ..AA] PRG-RAM Protect A
$5103: [.... ..BB] PRG-RAM Protect B
To allow writing to PRG-RAM you must set these regs to the following values:
A=%10
B=%01
Any other values will prevent PRG-RAM writing.
$5104: [.... ..XX] ExRAM mode
%00 = Extra Nametable mode ("Ex0")
%01 = Extended Attribute mode ("Ex1")
%10 = CPU access mode ("Ex2")
%11 = CPU read-only mode ("Ex3")
CHR Setup:
---------------------------
The MMC5 has two sets of CHR regs. One set is used for sprites, the other is used for BG. The MMC5
carefully watches what tiles are being fetched and when (or has some other way of syncing with the NES
somehow), which allows it to tell when the NES is fetching BG tiles, and when it's fetching sprite tiles.
As such, it can use different regs accordingly, allowing games to basically have 12k of CHR "active" at once
instead of the usual 8k! This means you can have a full 512 tiles exclusively for sprites, and have an
additional 256 tiles for the BG!
CHR Mode Select Reg:
$5101: [.... ..CC]
%00 = 8k Mode
%01 = 4k Mode
%10 = 2k Mode
%11 = 1k Mode
'High' CHR Reg:
$5130 [.... ..HH] (see below)
'A' Regs:
$5120 - $5127
'B' Regs:
$5128 - $512B
When in 8x16 sprite mode, both sets of registers are used. The 'A' set is used for sprite tiles, and the
'B' set is used for BG. This makes it so that sprites can have a full 8k of CHR available, without having
to share any of the tiles with the BG (since the BG uses it's own 4k of CHR, designated by the 'B' set). It
is unsure what you will get when reading CHR via $2007.
When in 8x8 sprite mode, only one set is used for both BG and sprites. Either 'A' or 'B', depending on which
set is written to last. If 'B' is used, $1000-1FFF always mirrors $0000-0FFF (making the 'B' set pretty
worthless with 8x8 sprites)
'A' Set (sprites):
$0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
+---------------------------------------------------------------+
C=%00: | $5127 |
+---------------------------------------------------------------+
C=%01: | $5123 | $5127 |
+-------------------------------+-------------------------------+
C=%10: | $5121 | $5123 | $5125 | $5127 |
+---------------+---------------+---------------+---------------+
C=%11: | $5120 | $5121 | $5122 | $5123 | $5124 | $5125 | $5126 | $5127 |
+-------+-------+-------+-------+-------+-------+-------+-------+
'B' Set (BG):
$0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
+-------------------------------+
C=%00: | $512B* |
+-------------------------------+
C=%01: | $512B |
+-------------------------------+ $1xxx always mirrors $0xxx
C=%10: | $5129 | $512B |
+---------------+---------------+
C=%11: | $5128 | $5129 | $512A | $512B |
+-------+-------+-------+-------+
* $512B in 8k mode is an 8k page number, but only the first half of the 8k page is used.
(It is not clear that the above is always true. It seems that neither nintendulator nor fceux actually obey this, and if they do, then bugs can be observed in quietust's "mmc5exram" copperbars demo. A proposed revision would be as follows: )
'B' Set (BG):
$0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
+-------------------------------+-------------------------------+
C=%00: | $512B |
+-------------------------------+-------------------------------+
C=%01: | $512B | $512B |
+-------------------------------+-------------------------------+
C=%10: | $5129 | $512B | $5129 | $512B |
+---------------+---------------+---------------+---------------+
C=%11: | $5128 | $5129 | $512A | $512B | $5128 | $5129 | $512A | $512B |
+-------+-------+-------+-------+-------+-------+-------+-------+
Note that unlike most other mappers, these CHR pages are in *actual* sizes. IE: when in 4k mode, registers
contain 4k page numbers. But when in 2k mode, register contain 2k page numbers.
CHR Regs are actually 10 bits wide, not just 8. When you write to the regs, the value written is the low 8
bits, and the high 2 bits are copied from $5130. Example:
LDA #$00
STA $5130 ; high bits = 0
LDA #$20
STA $5127 ; $5127 now = $020
LDA #$02
STA $5130
LDA #$41
STA $5123 ; $5123 now = $241
; and $5127 still = $020 (not $220)
$5130 has an additional role in ExAttribute mode.
PRG/RAM Setup:
---------------------------
$5100: [.... ..PP] PRG Mode Select:
%00 = 32k
%01 = 16k
%10 = 16k+8k
%11 = 8k
$5113: [.... .PPP] (simplified, but technically inaccurate -- see below)
8k PRG-RAM page @ $6000
$5114-5117: [RPPP PPPP]
R = ROM select (0=select RAM, 1=select ROM) **unused in $5117**
P = PRG page
The high bit allows the game to select between ROM and RAM. This allows the game to put PRG-RAM anywhere
between $6000-DFFF (but no higher, since $5117 always selects ROM)
Only RAM can be swapped to $6000-7FFF.
$5117 always selects ROM, never RAM (ROM always at $E000-FFFF).
$6000 $8000 $A000 $C000 $E000
+-------+-------------------------------+
P=%00: | $5113 | <<$5117>> |
+-------+-------------------------------+
P=%01: | $5113 | <$5115> | <$5117> |
+-------+---------------+-------+-------+
P=%10: | $5113 | <$5115> | $5116 | $5117 |
+-------+---------------+-------+-------+
P=%11: | $5113 | $5114 | $5115 | $5116 | $5117 |
+-------+-------+-------+-------+-------+
Technically, $5113 should look something like:
[.... .CPP]
C = Chip select
P = 8k PRG-RAM page on selected chip
MMC5 can address two seperate RAM chips, each up to 32k in size.
This detail can impact how RAM is mirrored across pages if the chip sizes are less than 32k. For example,
Uncharted Waters has two 8k chips (only 16k total -- but on two seperate chips), so it uses selects pages
$00 and $04, rather than $00 and $01 like you may expect. This is because bit 2 is the chip select, and
the 8k on each chip is mirrored to every page on that chip... that is... $00-$03 would all select the first
8k.
Note that no commercial games rely on this mirroring -- therefore you can take the easy way out and simply give
all MMC5 games 64k PRG-RAM.
Mirroring:
---------------------------
$5105: [DDCC BBAA]
MMC5 allows each NT slot to be configured:
[ A ][ B ]
[ C ][ D ]
Values can be the following:
%00 = NES internal NTA
%01 = NES internal NTB
%10 = use ExRAM as NT
%11 = Fill Mode
For example... some typical mirroring setups would be:
( D C B A)
Horz: $50 (%01 01 00 00)
Vert: $44 (%01 00 01 00)
1ScA: $00 (%00 00 00 00)
1ScB: $55 (%01 01 01 01)
ExRAM can act as a 3rd nametable here... but only in Ex0 or Ex1 (see $5104 above). If in Ex2 or Ex3, the PPU
will get $00 when it attempts to read from the nametable. Note that while ExRAM can be used as a nametable
in Ex1, it's probably a bad idea, since ExRAM is also used for Extended attributes in that mode. Therefore,
when using ExRAM as a nametable, you should stick to Ex0.
Fill Mode is a virtual nametable. It is not a full nametable, but rather, as the PPU attempts to read it,
the MMC5 will feed it a specific tile -- thus appearing as though there's a full nametable filled with a
single tile. The tile can be configured by the game with the following regs:
$5106: [TTTT TTTT] Fill Tile
$5107: [.... ..AA] Fill Attribute bits
Extended Attribute Mode:
---------------------------
When in Ex1 mode (see $5104 above), ordinary attribute tables and BG CHR regs are ignored, and instead, each
byte in ExRAM coresponds with an onscreen tile, and assigns that tile a 4k CHR page (allowing you to choose
from 16k tiles instead of 256) and its own attribute bits (allowing each 8x8 tile to have it's own palette,
rather than having the normal 16x16 blocks).
Bytes in ExRAM:
[AACC CCCC]
A = Attribute bits
C = 4k CHR Page
Additionally... $5130 is used directly as the high 2 bits of CHR for every on-screen BG tile when in this
mode. It effectively selects a 256k block for BG to use (in addition to its normal use with CHR swapping).
$5130's runtime value affects all BG tiles, therefore changing $5130 will immediately swap all on-screen BG
when in this mode. Therefore, if/when you change $5130 to swap CHR for sprites, you must write to $5130
again with the desired value for the BG.
Sprites are unaffected by this mode and still use the normal CHR regs.
Which tile uses which byte in ExRAM depends on its position in the nametable. Scrolling is irrelevent. The
tile at $2000 always uses the first byte in ExRAM, $2001 uses the second, etc. $2400, $2800, and $2C00 also
use the first byte of ExRAM.
CPU Accessing ExRAM:
---------------------------
ExRAM can be accessed by the CPU via $5C00-$5FFF. Whether or not you can read or write depends on the
current mode (see $5104):
Mode Readable Writable
-------------------------
Ex0 no *
Ex1 no *
Ex2 yes yes
Ex3 yes no
In Ex0 and Ex1, ExRAM can only be written DURING RENDERING (insane, I know). If a game attempts to write
outside of rendering, $00 is written instead of the desired value. Writes have absolutely no effect in Ex3.
Attempting to read when not readable will return open bus.
8 * 8 -> 16 Multiplier:
---------------------------
MMC5 has a nifty multiplier, similar to the SNES's.
on write:
$5205: multiplicand
$5206: multiplier
on read:
$5205: low 8 bits of product
$5206: high 8 bits of product
Basic functionality is, you write two values you want multiplied to $5205 and $5206, then read the product
back. Multiplication is unsigned. There is no noticable delay -- that is, the product can be read back
right after writing.
Split Screen:
---------------------------
A unique feature to MMC5 is its ability to split the screen vertically down the middle. However due to some
limitations that couldn't be avoided, it ended up not being that useful of a feature.
Note: Split screen mode is only allowed in Ex0 or Ex1. When in Ex2 and Ex3, it is always disabled. I do
not know whether or not the split is affected by Extended Attributes when in Ex1. Judging by the $5202, I
would assume it isn't, but that's a total guess.
$5200: [ER.T TTTT] Split control
E = Enable (0=split mode disabled, 1=split mode enabled)
R = Right side (0=split will be on left side, 1=split will be on right)
T = tile number to split at
$5201: [YYYY YYYY] Split Y scroll
$5202: [CCCC CCCC] 4k CHR Page for split
34 BG tiles are fetched per scanline. MMC5 performs the split by watching which BG tile is being fetched,
and if it is within the split region, replacing the normal NT data with the split screen data. Since it
operates on a per-tile basis... fine horizontal scrolling "carries into" the split region. Setting the
horizontal scroll to 1-7 will result in the split being moved to the left 1-7 pixels, however when you scroll
to 8, the split will "snap" back to its normal position.
Left Split:
Tiles 0 to T-1 are the split.
Tiles T and on are rendered normally.
Right Split:
Tiles 0 to T-1 are rendered normally.
Tiles T and on are the split.
There is no coarse horizontal scrolling of any kind for the split. Right-side splits will always show the
right-hand side of the nametable, and left-hand splits will always show the left-hand side of the nametable.
Coarse horizontal scrolling can still be used for the non-split region.
ExRAM is always used as the nametable in split screen mode.
Vertical scrolling for the split operates like normal vertical scrolling. 0-239 are valid scroll values,
whereas 240-255 will display Attribute table data as NT data for the first few scanlines. The split nametable
will wrap so that the top of the nametable will appear below as you scroll (just as if vertical mirroring
were employed).
$5202 selects (yet another) CHR page to use for the BG. This page is used for the split region only.
IRQ Operation:
---------------------------
MMC5 has a scanline counter for IRQs, however it is significantly more sophisticated than MMC3's, and doesn't
suffer from the same restrictions. It is also a bit easier to use.
Write:
$5203: [IIII IIII] IRQ Target
$5204: [E... ....] IRQ Enable (0=disabled, 1=enabled)
Read:
$5204: [PI.. ....]
P = IRQ currently pending
I = "In Frame" signal
Reading $5204 will clear the pending flag (acknowledging the IRQ).
Basic operation:
1) Write the desired scanline number to $5203
2) Enable IRQs by setting $5204.7
IRQ will then trip on the given scanline number (provided PPU rendering is enabled). The only thing to
note here is that this behavior changes drastically if you turn the PPU off mid-frame... and that an IRQ will
never occur when the target scanline number is 0 or greater than (?or equal to?) $F0.
The "In Frame" signal will read back as set when the PPU is rendering (during scanlines 0-239). Though
it's actual behavior and how it interacts with the IRQ counter is a bit more complex.
Detailed Operation:
The IRQ counter is an up counter, rather than a down counter (like MMC3). Every time the MMC5 detects a
scanline, it does the following:
- If In Frame Signal is clear...
a) Set In Frame signal
b) Reset IRQ counter to 0
c) Clear IRQ pending flag (automatically acknowledging IRQ)
- otherwise...
a) Increment IRQ counter
b) If IRQ counter now equals the trigger value, raise IRQ pending flag
Note that the IRQ pending flag is raised *regardless* of whether or not IRQs are enabled. However, this will
only trigger an IRQ on the 6502 if both this flag *and* the IRQ enable flag is set. Therefore IRQs must
still be enabled for this to have an effect, however the pending flag can still be read back as set via $5204
even when IRQs are disabled.
Also note that the IRQ counter is compared after it is incremented. This is why a trigger value of 0 will
never trigger an IRQ.
At any time when the MMC5 detects that the PPU is inactive, the In Frame signal is automatically cleared.
The MMC5 will detect this after rendering for the frame is complete, and as soon as the PPU is turned off via
$2001. This is why turning off the PPU mid-frame will disrupt IRQs -- since the In Frame signal being
cleared will reset the IRQ counter next scanline.
HOW the MMC5 detects scanlines is still unknown. One theory is that it looks for the two dummy nametable
fetches at the end of the scanline. Or perhaps it counts the number of fetches the PPU performs. Nobody
knows for sure.
The IRQ will trip at the *start* of the desired scanline. Or, more precisely, near the very end of the
previous scanline (closest I can figure is dot 336). That is... if the trigger line is set to 1, the IRQ
will trip on dot 336 of scanline 0.
I am unsure whether or not the last rendered scanline (239) is detected by the MMC5. I would assume it is,
which would mean a trigger value of $F0 would trip an IRQ at the end of rendering. Trigger values above $F0
will never be reached, since rendering stops before then, and the in-frame signal would automatically clear.
Sound:
---------------------------
The MMC5 also has 3 additional sound channels! (Will the list of features ever stop?!?!). Unfortunately,
due to the NES being dumbed down, these can only be heard on a Famicom (or a modified NES).
There are 2 additional Pulse channels, and 1 additional PCM channel.
Registers for them are as follows:
Write:
$5000-5003: Regs for Pulse 1
$5004-5007: Regs for Pulse 2
$5010: PCM Unknown (no games use this part of the PCM)
$5011: PCM output
$5015: [.... ..BA] Enable flags for Pulse 1 (A), 2 (B) (0=disable, 1=enable)
Read:
$5015 [.... ..BA] Length status for Pulse 1 (A), 2 (B)
Pulse channels behave identically to the native NES pulse channels, only they lack a sweep unit. Rather than
going into details on their function, I recommend you pick up blargg's apu reference.
$5000-5007 operate just as $4000-4007 do
$5015 operates just as $4015 does (for reads and writes)
Nobody knows exactly how the PCM channel of the MMC5 works. The patent documentation is unclear, and no
games seem to use it apart from $5011. $5010 likely does *something*... but nobody knows what.
$5011 operates exactly like $4011, only it is 8 bits wide instead of 7. Games *do* use this register to
output sound.
Powerup:
---------------------------
Games seem to expect $5117 to be $FF on powerup (last PRG page swapped in). Additionally, Romance of the 3
Kingdoms 2 seems to expect it to be in 8k PRG mode ($5100 = $03).
Register Overview:
---------------------------
Due to the massive number of registers on this mapper, this section will be brief. Registers were all
covered in detail in the sections above -- this is just to recap them all:
Writable Regs:
$5000-5003: Sound, Pulse 1
$5004-5007: Sound, Pulse 2
$5010-5011: Sound, PCM
$5015: Sound, General
$5100: PRG Mode Select
$5101: CHR Mode Select
$5102-5103: PRG-RAM Write protect
$5104: ExRAM Mode
$5105: Mirroring Mode
$5106: Fill Tile
$5107: Fill Attribute
$5113: PRG-RAM reg
$5114-5117: PRG regs
$5120-5127: CHR regs 'A'
$5128-512B: CHR regs 'B'
$5130: CHR high bits
$5200: Split Screen control
$5201: Split Screen V Scroll
$5202: Split Screen CHR Page
$5203: IRQ Trigger
$5204: IRQ Control
$5205-5206: 8*8->16 Multiplier
$5C00-5FFF: ExRAM CPU Access
Readable Regs:
$5015: Sound Status
$5204: IRQ Status
$5205-5206: 8*8->16 Multiplier Product
$5C00-5FFF: ExRAM CPU Access
