NES 2.0 Mapper 266: Difference between revisions
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[[Category:Mappers with cycle IRQs]]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'''. | {{DEFAULTSORT:266}}[[Category:Mappers with cycle IRQs]]'''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: | Mask: $F00C, see [[VRC2_and_VRC4#Mirroring_Control_.28.249000.2C_.249001.2C_.249002.2C_.249003.29|VRC4 description]]. | ||
== | ==PRG Select ($900C)== | ||
Mask: | 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: $F80C | |||
7654 3210 | D~7654 3210 | ||
--------- | |||
.... DDDD | |||
++++- 4 bit unsigned PCM data | |||
== | ==CHR Select ($A00x/$B00x/$D00x/$E00x)== | ||
Mask: | 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 | |||
==IRQ | $B008/$B00C (LSB/MSB): Select 1 KiB CHR-ROM bank at PPU $1400-$17FF | ||
Mask: | $E000/$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 [[VRC2_and_VRC4#IRQ_Control_.28.24F00x.29_VRC4|VRC4 description]]. | |||
=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. | |||
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.
