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| | #REDIRECT [[VRC2 and VRC4]] |
| [[Category:iNES Mappers|022]][[Category:in NesCartDB|022]] | | [[Category:iNES Mappers|022]][[Category:in NesCartDB|022]] |
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| [[iNES Mapper 022]] is used to represent the VRC2a variant of the Konami [[VRC2]] mapper (PCB '''351618''').
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| Here are Disch's original notes:
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| ========================
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| = Mapper 022 =
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| = + 023 =
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| = + 025 =
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| ========================
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|
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| aka
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| --------------------------
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| [[VRC2]]
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| Example Games:
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| --------------------------
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| Ganbare Pennant Race (022)
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| TwinBee 3 (022)
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| Wai Wai World (023)
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| Ganbare Goemon Gaiden (025)
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| Multiple numbers, just one mapper:
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| --------------------------
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| These mapper numbers (022, 023) represent 2 wiring variations of the same mapper: VRC2. Each variation
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| operates the same, only the registers used are different because their lines are reversed from each other:
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| variant lines registers Mapper Number
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| =================================================================
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| VRC2a: A1, A0 $x000, $x002, $x001, $x003 022 * divides CHR bank select by two
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| VRC2b: A0, A1 $x000, $x001, $x002, $x003 023
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| VRC2c: A1, A0 $x000, $x002, $x001, $x003 025 * does NOT divide CHR bank select by two
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| This doc will use the 'VRC2b' registers (0,1,2,3) in all following register descriptions. For 'VRC2a',
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| simply reverse $x001 and $x002 registers.
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| VRC2a CHR:
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| ---------------------------
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| Important note! On VRC2a (mapper 022) only the high 7 bits of the CHR regs are used -- the low bit is
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| ignored. Therefore, you effectively have to right-shift the CHR page by 1 to get the actual page number.
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| For example... both $06 and $07 would both indicate page $03
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| This applies to VRC2a only. VRC2b (mapper 023) behaves normally.
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| VRC2 vs. VRC4:
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| --------------------------
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| VRC2 is strikingly similar to VRC4 (see mapper 021). The differences are:
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| 1) VRC4 has IRQs, VRC2 does not
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| 2) VRC4 has 5 bits for PRG regs, VRC2 only has 4 bits
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| 3) VRC4 has 2 PRG modes, VRC2 does not.
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| Those differences aside -- they act exactly the same.
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| Registers:
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| --------------------------
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| Some registers are mirrored across several addresses. For example, writing to $8003 has the same effect as
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| writing to $8000.
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| $8000-$8003: [.... PPPP] PRG Reg 0 (select 8k @ $8000)
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| $9000-$9003: [.... ..MM] Mirroring:
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| %00 = Vert
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| %01 = Horz
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| %10 = 1ScA
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| %11 = 1ScB
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| $A000-$A003: [.... PPPP] PRG Reg 1 (select 8k @ $A000)
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| $B000-$E003: [.... CCCC] CHR Regs (see CHR Setup)
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| PRG Setup:
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| --------------------------
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| $8000 $A000 $C000 $E000
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| +-------+-------+-------+-------+
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| | $8000 | $A000 | { -2} | { -1} |
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| +-------+-------+-------+-------+
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| CHR Setup:
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| --------------------------
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| The VRC2 only has 4 data pins for CHR Regs. To compensate, two CHR regs are combined to form a single page
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| number. One reg contains the high 4 bits and the other reg contains the low 4 bits (allowing for 8-bit page
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| numbers)
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| Example: $B000+$B001 select 1k CHR page @ $0000
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| if $B000=$03
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| and $B001=$01
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| then use page $13 (VRC2b)
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| or page $09 (VRC2a -- see notes above)
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| $0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
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| +-------+-------+-------+-------+-------+-------+-------+-------+
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| |$B000+1|$B002+3|$C000+1|$C002+3|$D000+1|$D002+3|$E000+1|$E002+3|
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| +-------+-------+-------+-------+-------+-------+-------+-------+
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