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