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| [[Category:iNES Mappers|028]][[category:Mappers using $4020-$5FFF]]
| | #REDIRECT [[Action 53 mapper]] |
| '''iNES Mapper 028''' is assigned to a [[User:Tepples/Multi-discrete mapper|multicart mapper]] developed by Tepples and Infiniteneslives in October 2012, as an extension of the [[Action 53]] project to cover [[CNROM]] and [[UNROM]] games.
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| It is used for ''STREEMERZ: Action 53 Function 16 Volume One'' and ''Double Action 53''.
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| Implemented in FCEUX as of r2739 ([https://sourceforge.net/p/fceultra/bugs/550/ tracking bug]) but appears to have been dropped sometime between 2.2.0 and 2.2.1.
| | [[Category:iNES Mappers|028]] {{DEFAULTSORT:028}} [[category:Mappers using $4020-$5FFF]] |
| Implemented in Bizhawk as of r3680.
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| == Disch ==
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| Aping [[iNES Mapper DischDocs|Disch's style]]:
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| <pre>
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| ========================
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| = Mapper 028 =
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| ========================
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| aka
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| --------------------------
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| Multi-discrete
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| Example Games:
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| --------------------------
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| Action 53 series
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| Notes:
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| --------------------------
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| This mapper is designed for making multicarts of games that
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| use NROM, CNROM, UNROM, BNROM, or AOROM. It looks like the
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| love child of MMC3, MMC1, and the Nintendo discrete mappers.
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| It has separate address and data ports like MMC3 (and FME-7),
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| its mode register is laid out in a way reminiscent of MMC1,
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| and it has the data port at $8000-$FFFF for compatibility with
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| the discrete mappers that it is designed to simulate.
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| Registers:
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| --------------------------
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| Range,Mask: $5000-$5FFF, $F000
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| $5000: [A... ...A] Address for use with $8000
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| Range,Mask: $8000-$FFFF, $8000
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| $8000: [..DD DDDD] Data port
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| R:$00 -> CHR Reg
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| R:$01 -> PRG Reg
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| R:$80 -> Mode
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| R:$81 -> Outer PRG Reg
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| These registers are internal, written through the data port:
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| R:$00: [...M ..CC]
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| C = CHR Reg
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| M = Mirroring
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| This bit overwrites bit 0 of R:$80, but only if bit 1 of
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| R:$80 is clear
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| R:$01: [...M PPPP]
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| P = PRG Reg
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| M = Mirroring
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| This bit overwrites bit 0 of R:$80, but only if bit 1 of
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| R:$80 is clear
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| R:$80: [..GG PSMM]
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| G = Game Size (0=32K, 1=64K, 2=128K, 3=256K)
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| P = PRG Size (0=32k mode, 1=16k mode)
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| S = Slot select:
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| 0 = $C000 swappable, $8000 fixed to bottom of 32K outer bank
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| 1 = $8000 swappable, $C000 fixed to top of 32K outer bank
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| This bit is ignored when 'P' is clear (32k mode)
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| M = Mirroring control:
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| %00 = 1ScA
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| %01 = 1ScB
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| %10 = Vert
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| %11 = Horz
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| R:$81: [..BB BBBB]
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| Outer PRG Reg
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| CHR Setup:
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| ---------------------------
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| $0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
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| +---------------------------------------------------------------+
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| | R:$00 |
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| +---------------------------------------------------------------+
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| PRG Setup:
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| ---------------------------
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| There is 1 PRG reg and 3 PRG modes, corresponding to mappers 34, 2,
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| and 180. When 32K PRG mode is used (P = 0), R:$01 specifies a 32K
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| bank number between 0 and 7 (i.e., the high bit is ignored). When
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| 16K PRG mode is used (P = 1), R:$01 specifies a 16K bank number
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| between 0 and F.
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| $8000 $A000 $C000 $E000
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| +-------------------------------+
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| P = 0: | R:$01 |
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| +-------------------------------+
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| P = 1, S = 0: | "Fixed" | R:$01 |
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| +---------------+---------------+
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| P = 1, S = 1: | R:$01 | "Fixed" |
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| +---------------+---------------+
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| The "fixed" banks aren't really fixed. They represent the first and
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| second half of the currently selected outer bank, as if temporarily
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| forcing P=0 and G=0 for a single read.
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| The 4-bit output I (Inner) from this phase tells which 16K bank within a
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| single game is being read. The value is fed into the multicart logic.
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| The game size G controls how many bits of I are kept, the rest being
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| replaced with bits of the outer bank number O = 2 * R:$81. This can
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| be thought of as an inner-AND and outer-AND value controlled by G.
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| I is ANDed with inner-AND, O is ANDed with outer-AND, and the results
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| are ORed to form a 16K page number.
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| 'G' Block size Inner-AND Outer-AND
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| ----------------------------------------
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| 0 32K $01 $7E
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| 1 64K $03 $7C
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| 2 128K $07 $78
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| 3 256K $0F $70
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| This 16K page number is concatenated with bits A13-A0 to form the
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| PRG ROM address.
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| An easy way to visualize the 16K bank number in 16K PRG mode is as
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| follows:
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| B5 B4 B3 B2|B1 B0 Outer PRG bits from R:$81
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| P3|P2 P1 P0 Inner PRG bits from R:$01
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| The location of the separator is determined by the game size selected
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| in R:$80. The above separator location corresponds to 128K. Moving
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| the separator one step to the left or right would be 256K and 64K,
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| respectively. The 16K bank number is formed by the outer PRG bits to
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| the left of the separator and the inner PRG bits to the right, giving
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| the bank number B5 B4 B3 B2 P2 P1 P0 in this example.
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| The only difference in 32K PRG mode is that the inner PRG bits are
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| shifted one step to the left:
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| B5 B4 B3 B2|B1 B0 Outer PRG bits from R:$81
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| P3 P2|P1 P0 x Inner PRG bits from R:$01
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| This gives the 16K bank number B5 B4 B3 B2 P1 P0 x, where x = 0 is
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| the lower 16K part of the 32K bank and x = 1 the higher 16K part.
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|
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| Powerup and Reset:
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| ---------------------------
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| The last 16K PRG bank is switched into $C000-$FFFF on powerup.
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| Registers are unchanged on reset.
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| </pre>
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| == References ==
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| *[http://forums.nesdev.org/viewtopic.php?p=101111#p101111 Forum post announcing reservation of #28]
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| *[http://forums.nesdev.org/viewtopic.php?p=101970#p101970 Forum post announcing implementation in NESICIDE]
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