|
|
| (One intermediate revision by one other user not shown) |
| Line 1: |
Line 1: |
| [[Category:iNES Mappers|024]][[Category:in NesCartDB|024]] | | #REDIRECT [[VRC6]] |
|
| |
|
| [[iNES Mapper 024]] is used to represent one variant of the Konami [[VRC6]] mapper (PCB '''351951'''). | | {{DEFAULTSORT:024}}[[Category:iNES Mappers]][[Category:in NesCartDB]][[Category:Mappers with cycle IRQs]] |
| | |
| Here are Disch's original notes:
| |
| ========================
| |
| = Mapper 024 =
| |
| = + 026 =
| |
| ========================
| |
|
| |
| aka
| |
| --------------------------
| |
| VRC6
| |
|
| |
|
| |
|
| |
| Example Games:
| |
| --------------------------
| |
| Akumajou Densetsu (024)
| |
| Madara (026)
| |
| Esper Dream 2 (026)
| |
|
| |
|
| |
|
| |
| Multiple numbers, just one mapper:
| |
| --------------------------
| |
| As is the VRC way... VRC6 comes in two varieties. Both variants operate exactly the same, only the reigster
| |
| addresses are different:
| |
|
| |
| variant lines registers Mapper Number
| |
| =================================================================
| |
| VRC6a: A0, A1 $x000, $x001, $x002, $x003 024
| |
| VRC6b: A1, A0 $x000, $x002, $x001, $x003 026
| |
|
| |
|
| |
|
| |
| This doc will use the 'VRC6a' registers (0,1,2,3) in all following register descriptions. For 'VRC6b',
| |
| simply reverse $x001 and $x002.
| |
|
| |
|
| |
| Registers:
| |
| --------------------------
| |
| Some registers are mirrored across several addresses. For example, writing to $8003 has the same effect as
| |
| writing to $8000.
| |
|
| |
| $8000-$8003: [PPPP PPPP] PRG Reg 0 (Select 16k @ $8000)
| |
| $9000-$9002: Sound, Pulse 1 (see sound section)
| |
| $A000-$A002: Sound, Pulse 2
| |
| $B000-$B002: Sound, Sawtooth
| |
| $B003: [.... MM..] Mirroring:
| |
| %00 = Vert
| |
| %01 = Horz
| |
| %10 = 1ScA
| |
| %11 = 1ScB
| |
|
| |
| $C000-$C003: [PPPP PPPP] PRG Reg 1 (Select 8k @ $C000)
| |
| $D000-$E003: [CCCC CCCC] CHR regs (See CHR setup)
| |
| $F000-$F002: IRQ regs (See IRQ section)
| |
|
| |
|
| |
| PRG Setup:
| |
| --------------------------
| |
|
| |
| $8000 $A000 $C000 $E000
| |
| +---------------+-------+-------+
| |
| | $8000 | $C000 | { -1} |
| |
| +---------------+-------+-------+
| |
|
| |
|
| |
| CHR Setup:
| |
| --------------------------
| |
|
| |
| $0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
| |
| +-------+-------+-------+-------+-------+-------+-------+-------+
| |
| | $D000 | $D001 | $D002 | $D003 | $E000 | $E001 | $E002 | $E003 |
| |
| +-------+-------+-------+-------+-------+-------+-------+-------+
| |
|
| |
|
| |
| IRQs:
| |
| --------------------------
| |
|
| |
| VRC6 use the "VRC IRQ" setup shared by several VRCs. It uses the following registers:
| |
|
| |
|
| |
| $F000: [IIII IIII] IRQ Reload
| |
| $F001: [.... .MEA] IRQ Control
| |
| $F002: [.... ....] IRQ Acknowledge
| |
|
| |
| For info on how these IRQs work, see the "VRC IRQs" section in mapper 021
| |
|
| |
|
| |
| ==========================
| |
| Sound:
| |
| --------------------------
| |
|
| |
| VRC6 has two additional pulse channels, and one sawtooth channel. Both operate very similarly to the NES's
| |
| native channels.
| |
|
| |
|
| |
|
| |
| Pulse Channels:
| |
| ------------------------
| |
|
| |
| $9000, $A000: [MDDD VVVV]
| |
| M = Mode (0=normal mode, 1=digitized mode)
| |
| D = Duty cycle (duty cycle is (D+1)/16)
| |
| V = Volume
| |
|
| |
| $9001, $A001: [FFFF FFFF]
| |
| F = Low 8 bits of Frequency
| |
|
| |
| $9002, $A002: [E... FFFF]
| |
| F = High 4 bits of Frequency
| |
| E = Channel Enable (0=disabled, 1=enabled)
| |
|
| |
|
| |
| Pulse 1 uses regs $900x
| |
| Pulse 2 uses regs $A00x
| |
|
| |
|
| |
| Just like the NES's own pulse channels, an internal counter is counted down each CPU cycle, and when it
| |
| wraps, it's reloaded with the 'F' frequency value, and the duty cycle unit takes another step. VRC6's pulses
| |
| can have a duty cycle anywhere between 1/16 and 8/16 depending on the given 'D' value.
| |
|
| |
| Channel output is either 0 or 'V', depending on the current state of the duty cycle unit (or digitized
| |
| mode).
| |
|
| |
| When 'M' is set (digitized mode), the duty cycle is ignored, and 'V' is always output. In this mode, the
| |
| channel essentially is no longer a Pulse wave, but rather $9000/$A000 acts like a 4-bit PCM streaming
| |
| register (similar to $4011).
| |
|
| |
| When 'E' is clear (channel disabled), output of the channel is forced to '0' (silencing the channel).
| |
|
| |
| Generated tone in Hz can be calculated by the following:
| |
|
| |
| CPU_CLOCK
| |
| Hz = -------------
| |
| (F+1) * 16
| |
|
| |
|
| |
| Sawtooth Channel:
| |
| ------------------------
| |
|
| |
| $B000: [..AA AAAA]
| |
| A = Accum Rate
| |
|
| |
| $B001: [FFFF FFFF]
| |
| F = Low 8 bits of frequency
| |
|
| |
| $B002: [E... FFFF]
| |
| F = High 4 bits of frequency
| |
| E = Channel Enable (0=disabled, 1=enabled)
| |
|
| |
|
| |
| The sawtooth uses an 8-bit accumulation register. Every time it is clocked, 'A' is added until the 7th
| |
| clock, at which point it is reset to 0. The high 5 bits of this accumulation reg are then used as the
| |
| channel output. Strangely, though, the accumulation register seems to only be clocked once for every *two*
| |
| times the frequency divider expires. This results in a tone that's an octave lower than you might expect.
| |
|
| |
| It's difficult to put in words, so here's an example using $0B as a value for the accum rate ('A'):
| |
|
| |
| Step Accum. Channel output
| |
| -------------------------------
| |
| 0 $00 $00
| |
| 1 $00 $00 odd steps do nothing
| |
| 2 $0B $01 even steps.. add value of 'A' to accum
| |
| 3 $0B $01
| |
| 4 $16 $02
| |
| 5 $16 $02
| |
| 6 $21 $04
| |
| 7 $21 $04
| |
| 8 $2C $05
| |
| 9 $2C $05
| |
| 10 $37 $06
| |
| 11 $37 $06
| |
| 12 $42 $08 6th and final time 'A' is added
| |
| 13 $42 $08
| |
| 0 $00 $00 7th time, accum is reset instead
| |
| ... and the process repeats
| |
|
| |
| Channel output is the high 5 bits of the accumulation reg (right shift reg by 3). If the accum rate is too
| |
| high, the accum reg WILL wrap at 8 bits, causing ugly distortion. The highest accum rate you can use without
| |
| wrapping is $2A.
| |
|
| |
| If 'E' is clear (channel disabled), channel output is forced to 0 (silencing the channel).
| |
|
| |
| Generated tone in Hz can be calculated by the following:
| |
|
| |
| CPU_CLOCK
| |
| Hz = -------------
| |
| (F+1) * 14
| |
