INES Mapper 019
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Here are Disch's original notes:
========================
= Mapper 019 =
= + 210 =
========================
aka
--------------------------
Namcot 106
N106
Example Games:
--------------------------
Digital Devil Story - Megami Tensei 2 (019)
Final Lap (019)
Rolling Thunder (J) (019)
Splatter House (019)
Mappy Kids (019)
Family Circuit '91 (210)
Wagyan Land 2,3 (210)
Dream Master (210)
General Notes:
--------------------------
For a while, this mapper number was shared with 210. Therefore, there are a lot of ROMs floating around that
are labelled as mapper 019 that are really mapper 210.
Some games require CHR-RAM in addition to any CHR-ROM present. I'm uncertain exactly how much, but giving
them 8k seems to work.
Mapper 019 also has an additional 128 bytes of Sound RAM, which is used for waveform tables and sound
registers. Kaijuu Monogatari uses this as battery backed SRAM.
The rest of the doc applies to both mapper numbers. Differences between the two (mirroring and sound) will
be noted where appropriate.
Registers:
--------------------------
Range,Mask: $4800-FFFF, $F800
Writable and Readable:
$4800: [DDDD DDDD] Sound Data port (see Sound section for details)
(mapper 019 only)
$5000: [IIII IIII] Low 8 bits of IRQ counter
$5800: [EIII IIII]
E = IRQ Enable (0=disabled, 1=enabled)
I = High 7 bits of IRQ counter
$6000-7FFF: mapped to PRG-RAM, not registers
Writable only:
$8000-B800: CHR Regs
$C000-D800: Mirroring Regs (mapper 019 only)
$E000: [..PP PPPP] PRG Reg 0 (8k @ $8000)
$E800: [HLPP PPPP]
H = High CHR RAM Disable (see CHR setup for details)
L = Low CHR RAM Disable
P = PRG Reg 1 (8k @ A000)
$F000: [..PP PPPP] PRG Reg 2 (8k @ $C000)
$F800: [IAAA AAAA] Sound Address (with auto-increment enable bit)
(See Sound section for details) (mapper 019 only)
PRG Setup:
--------------------------
$8000 $A000 $C000 $E000
+-------+-------+-------+-------+
| $E000 | $E800 | $F000 | { -1} |
+-------+-------+-------+-------+
CHR Setup:
--------------------------
$0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
+-------+-------+-------+-------+-------+-------+-------+-------+
| $8000 | $8800 | $9000 | $9800 | $A000 | $A800 | $B000 | $B800 |
+-------+-------+-------+-------+-------+-------+-------+-------+
Page numbers lower than $E0 will select CHR-ROM. Page numbers greater than or equal to $E0 will select
CHR-RAM (RAM page N - $E0) *unless* CHR-RAM for the region is disabled via the appropriate bit in $E800.
$E800.6, when set, disables RAM selection for $0xxx ($8000-9800 will always select ROM)
$E800.7, when set, disables RAM selection for $1xxx ($A000-B800 will always select ROM)
CHR-RAM disable allows games to utilize all 256k of CHR-ROM. When CHR-RAM is enabled, only 224k can be
accessed.
Mirroring:
--------------------------
This section applies to mapper 019 only. 210 has hardwired mirroring
[ $C000 ][ $C800 ]
[ $D000 ][ $D800 ]
Values less than $E0 select a CHR-ROM page for a NT. Values $E0 and up use NES's internal nametables
(low bit selects which).
Typical Examples:
$C000 $C800 $D000 $D800
-----------------------
Horz: $E0 $E0 $E1 $E1
Vert: $E0 $E1 $E0 $E1
IRQ Operation:
--------------------------
IRQs are driven by a 15-bit CPU cycle up-counter. $5000 and $5800 are *direct* access to the IRQ counter
(they are not a reload value). Games can also read back the real-time state of the IRQ counter by reading
those regs.
When IRQs are enabled, the following occurs every CPU cycle:
- If IRQ Counter = $7FFF
a) Trip IRQ
- otherwise...
a) Increment IRQ counter by 1
Reading/Writing $5000 or $5800 will acknowledge the pending IRQ.
Sources on the behavior of this IRQ counter vary. Some say that the IRQ counter wraps from $7FFF to $0000,
and trips an IRQ only when it wraps -- however Sangokushi 2 polls $5800, and emulating IRQs that way results
in the game locking up shortly after it starts (once it sees that $5800 is not what it expects, it resets the
IRQ counter and loops)
Emulating the IRQ counter as above seems to work for every game out there -- although it probably isn't 100%
accurate.
Sound:
--------------------------
Sound applies to mapper 019 only. Mapper 210 has no extra sound.
N106 has some pretty sweet expansion sound. And it's used in several games to boot! (More than any other
expansion except for FDS)
The N106 has up to 8 additional sound channels, each which plays back a configurable waveform of variable
length, as well as having full volume control for each channel.
There are 128 bytes of Sound RAM inside the N106 which is used to hold the waveform data, as well as sound
registers. This RAM is accessed by setting the desired address by writing to $F800, then writing the
desired data to $4800. $4800 is also readable.
$F800: [IAAA AAAA]
I = Auto-increment flag
A = Sound RAM Address
If the auto-increment flag is set, the Sound RAM address will increment (wrapping $7F->00) after every $4800
read/write.
Sound Channel registers (inside Sound RAM):
regs: "A" "B" "C" "D" "E"
------------------------------
Ch 0 - $40 $42 $44 $46 $47
Ch 1 - $48 $4A $4C $4E $4F
Ch 2 - $50 $52 $54 $56 $57
Ch 3 - $58 $5A $5C $5E $5F
Ch 4 - $60 $62 $64 $66 $67
Ch 5 - $68 $6A $6C $6E $6F
Ch 6 - $70 $72 $74 $76 $77
Ch 7 - $78 $7A $7C $7E $7F
"A": [FFFF FFFF] Low 8 freq bits
"B": [FFFF FFFF] Mid 8 freq bits
"C": [...L LLFF]
F = High 2 freq bits
L = Instrument Length (4 * (8-L))
"D": [AAAA AAAA] Instrument address
"E": [.... VVVV] Volume
Special Reg $7F:
[.EEE VVVV]
E = Number of Enabled channels (E+1)
V = Channel 7's volume control
Instruments:
Instruments are in 4-bit samples. Each byte in sound RAM represents two samples (low 4 bits being the first
sample, high 4 bits being the second sample). Each channel has an address which it uses to look for the
instrument ('A' bits in reg "D"), as well as a length indicating how many samples are in the instrument ('L'
bits in reg "C").
The instrument address is in 4-bit samples. IE: When the instrument address is $20, the instrument starts
at the low 4 bits of byte address $10. A instrument address of $41 would be the high 4 bits of byte address
$20.
Instrument Length is 4 * (8-L) 4-bit samples. Therefore if L=3, the instrument is 20 4-bit samples long.
Samples are unsigned: '0' is low, 'F' is high.
For an example waveform... given the following instrument:
$A8 DC EE FF FF EF DE AC 58 23 11 00 00 10 21 53 (length of 32 ... L=0)
The following waveform (a pseudo-sine wave) would be produced:
F - *****
E - ** **
D - * *
C - * *
B -
A - * *
9 -
8 - * *
7 -
6 -
5 - * *
4 -
3 - * *
2 - * *
1 - ** **
0 - *****
__________________________________
The waveform would continually loop this pattern
Channel Disabling:
Reg $7F controls the number of enabled channels. As little as 1 or as many as all 8 channels can be enabled.
When not all channels are enabled, the high channels are the ones being used. That is, if only 3 channels
are enabled, channels 5, 6, and 7 are the ones enabled, and the others are disabled.
Disabling channels frees up more Sound RAM space for instruments (since the lower channels' registers are
unused when disabled). Also, since there are fewer channels to clock, the enabled channels are clocked more
quickly, resulting in higher quality sound and potentially higher tones (see frequency calculation)
Frequency Calculation:
The generated tone of each channel can be calculated with the following formula:
F * CPU_CLOCK
Hz = --------------------------
$F0000 * (E+1) * (8-L)*4
where:
F = the 18-bit Freq value
CPU_CLOCK = CPU clock rate (1789772.727272 on NTSC)
E = Enabled Channels (bits as written to reg $7F)
L = Instrument Length (bits as written)
Or... you can figure it as the number of CPU cycles that have to pass before the channel takes the next
step through its instrument:
$F0000 * (E+1)
Cycs = ------------------
F
When F is 0, the channel is essentially "frozen" at it's current position and does not update (and thus,
becomes silent).
