NES 2.0 Mapper 594
NES 2.0 Mapper 594 denotes the combination of Rinco Talkman 3-in-1 multicart (PSG code FSG2) using the enhanced audio features of Rinco's Talkman RS-7600 famiclone console.
Hardware overview
- 3 MiB of PRG-ROM, spread across a 2 MiB and a 1 MiB chip
- 1 MiB of CHR-ROM
- CPU $8000-$FFFF mapped by MMC3 clone from 512 KiB window into the 3 MiB of PRG-ROM
- CPU $6000-$7FFF mapped by discrete chips into the entire PRG-ROM address space
- PPU $0000-$1FFF mapped either like INES Mapper 187 (512 KiB window) or like normal MMC3 (256 KiB window)
- The 6502 program sends ADPCM data to an Advanced Micro Devices Am7202A 1024-byte FIFO until it is at least half full
- The FIFO serves an OKI MSM6585 ADPCM IC
Registers
These registers exist in addition or, where their address ranges would overlap, in lieu of the standard MMC3 registers.
Extra Bank ($9000, write)
D~[BBBB BBBB] (Address AND $F001)=$9000 ++++-++++-- PRG A20..A13
Selects the 8 KiB bank number that is mapped to CPU $6000-$7FFF. Up to an entire 2 MiB are accessible, depending on the register $B000 configuration, while the MMC3 can only address 512 KiB. The respective 2 MiB and 512 KiB address spaces are set by register $B000.
Unknown Register ($9001, write)
D~[...? ....] (Address AND $F001)=$9001
The function of this register is not known; the three games always write $10 to $9001 before writing to $9000.
Address Space and Mode ($B000, write)
D~[BB.. ....] (Address AND $F000)=$B000 ++--------- PRG and CHR address space and mode
Meanining of the BB bits:
00: Extra Bank addresses PRG $000000-$1FFFFF
MMC3 addresses PRG $000000-$07FFFF
and CHR $00000-$3FFFF (PPU $0000-$0FFF)
and CHR $40000-$7FFFF (PPU $1000-$1FFF)
40: Extra Bank addresses PRG $180000-$1FFFFF
MMC3 addresses PRG $180000-$1FFFFF
and CHR $80000-$BFFFF (PPU $0000-$1FFF)
80: Extra Bank addresses PRG $200000-$2FFFFF
MMC3 addresses PRG $200000-$27FFFF
and CHR $C0000-$FFFFF (PPU $0000-$1FFF)
FIFO Data ($5000, write)
D~[DDDD DDDD] (Address AND $F001)=$5000 ++++-++++-- ADPCM data byte
Writes a data byte into the 1024-byte FIFO. Probably only a good idea if the FIFO isn't full.
FIFO Reset and ADPCM Playback Rate($5001, write)
D~[DD.. ..] (Address AND $F001)=$5001
++--------- Playback Rate
0: 4 kHz
1: 8 kHz
2: 16 kHz
3: 32 kHz
Writing to this register empties the FIFO and sets the sampling rate of the OKI MSM6585.
FIFO Status ($5001, read)
D~[?D?? .....] (Address AND $F001)=$5001
+---------- FIFO half-full status
0=FIFO at least half-full
1=FIFO not at least half full
Games keep writing bytes to the FIFO as long as bit 6 is set. Since this register exists in the Rinco console, and a normal console returns open bus on reads with bit 6 set, games will never exit the "fill-FIFO" loop on a normal console.
