NES 2.0 Mapper 266: Difference between revisions
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--------- | --------- | ||
.... PP.. | .... PP.. | ||
++--- | ++--- PRG A16..A15 | ||
Similar to [[INES Mapper 189]], VRC4's fine-grained PRG banking is replaced with a single 32 KiB bank switch. | Similar to [[INES Mapper 189]], VRC4's fine-grained PRG banking is replaced with a single 32 KiB bank switch. | ||
| Line 29: | Line 29: | ||
++++- 4 bit unsigned PCM data | ++++- 4 bit unsigned PCM data | ||
==CHR Select ($A00x/$B00x/$D00x/$ | ==CHR Select ($A00x/$B00x/$D00x/$E00x)== | ||
Mask: $ | Mask: $F00C | ||
$D000/$D004 (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $0000-$03FF | $D000/$D004 (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $0000-$03FF | ||
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=Notes= | =Notes= | ||
[[File:City_fighter_4_dac_audio.png|thumb|Captured waveform of the audio speech when using R-2R as DAC]] | |||
The game uses the VRC4's pseudo-scanline mode during speech output. FCEUX only emulates a downward-counting CPU cycle counter, counting on every other cycle, causing speech to be played at too low a pitch compared to hardware. | The game uses the VRC4's pseudo-scanline mode during speech output. FCEUX only emulates a downward-counting CPU cycle counter, counting on every other cycle, causing speech to be played at too low a pitch compared to hardware. | ||
Latest revision as of 21:06, 1 June 2021
NES 2.0 Mapper 266 is used by City Fighter IV, a hack of Master Fighter II that adds (very grungy) PCM speech output. Given that its resolution (four bits) is worse than the NES/Famicom's own DAC at $4011 (seven bits), it's not immediately obvious what the purpose of including its own DAC is, other than perhaps the possibility of low-pass filtering the 3.5 kHz-sampled PCM data on the circuit board. Its UNIF board name is UNL-CITYFIGHT.
The circuit board mounts a VRC4 clone (A2/A3) with two of its higher CPU address lines mixed up:
CPU A3 -> VRC4 CPU Ax (pin 03) CPU A2 -> VRC4 CPU Ay (pin 04) CPU A13 -> VRC4 CPU A14 (pin 02) CPU A14 -> VRC4 CPU A13 (pin 01)
... and two additional registers that are selected via the VRC4 /WR9003 pin, e.g. by writing to $900C, and distinguished via CPU A11 ($0800). This results in the following effective registers:
Mirroring Control ($9000)
Mask: $F00C, see VRC4 description.
PRG Select ($900C)
Mask: $F80C
D~7654 3210
---------
.... PP..
++--- PRG A16..A15
Similar to INES Mapper 189, VRC4's fine-grained PRG banking is replaced with a single 32 KiB bank switch.
DAC Output ($980C)
Mask: $F80C
D~7654 3210
---------
.... DDDD
++++- 4 bit unsigned PCM data
CHR Select ($A00x/$B00x/$D00x/$E00x)
Mask: $F00C $D000/$D004 (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $0000-$03FF $D008/$D00C (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $0400-$07FF $A000/$A004 (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $0800-$0BFF $A008/$A00C (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $0C00-$0FFF $B000/$B004 (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $1000-$13FF $B008/$B00C (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $1400-$17FF $E000/$E004 (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $1800-$1BFF $E008/$E00C (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $1C00-$1FFF
IRQ Control ($F00x)
Mask: $F00C, see VRC4 description.
Notes
The game uses the VRC4's pseudo-scanline mode during speech output. FCEUX only emulates a downward-counting CPU cycle counter, counting on every other cycle, causing speech to be played at too low a pitch compared to hardware.
