INES Mapper 246
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Here are Disch's original notes: ======================== = Mapper 246 = ======================== Example Game: -------------------------- Fong Shen Bang - Zhu Lu Zhi Zhan Notes: -------------------------- Regs lie at $6000-67FF, but SRAM exists at $6800-7FFF. Don't know if there's only 6k of SRAM, or if there's 8k, but the first 2k is inaccessable. I find the latter more likely. Registers: --------------------------- Range,Mask: $6000-67FF, $6007 $6000-6003: PRG Regs $6004-6007: CHR Regs CHR Setup: --------------------------- $0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00 +---------------+---------------+---------------+---------------+ | $6004 | $6005 | $6006 | $6007 | +---------------+---------------+---------------+---------------+ PRG Setup: --------------------------- $8000 $A000 $C000 $E000 +-------+-------+-------+-------+ | $6000 | $6001 | $6002 | $6003 | +-------+-------+-------+-------+ Powerup/Reset: --------------------------- $6003 set to $FF on powerup (and probably reset, but not sure).
The present hardware seems to be:
- Four 74LS670 4 x 4bit dual-ported memory
- One GAL16V8
- PRG ROM (up to 2 MiB), CHR ROM (up to 512 KiB), PRG RAM (8 KiB)
- Miscellaneous resistors, diodes, and a battery to power the PRG RAM
Correspondingly, it seems more likely that:
- all four PRG banks are $FF on powerup, but all go to whatever the value in the 74LS670s is after some unknown event (the first write?)
- More PRG RAM may be accessible (up to 8176 bytes) and there are probably fewer mirrors of the registers
See also:
- http://forums.nesdev.org/viewtopic.php?t=13969 Why does Fong Shen Bang only work in Famiclones?