INES Mapper 178
iNES Mapper 178 is used by some games from Waixing and Henge Dianzi as well as some educational computers. It always uses CHR-RAM and can use up to 32 KiB of PRG-RAM, banked in 8 KiB amounts.
Mode Register ($4800)
7654 3210 --------- .... .PPM ||+- Select nametable mirroring type || 0: Vertical || 1: Horizontal ++-- Select PRG banking mode 0: 32 KiB PRG-ROM bank at CPU $8000-$FFFF, low bank bit 0 ignored 1: 16 KiB PRG-ROM bank at CPU $8000-$BFFF comprised of selectable high and low banks 16 KiB PRG-ROM bank at CPU $C000-$FFFF comprised of selectable high and fixed low bank 7 2: 16 KiB PRG-ROM bank at CPU $8000-$BFFF comprised of selectable high and low banks 16 KiB PRG-ROM bank at CPU $C000-$FFFF being a mirror of $8000-$BFFF 3: 16 KiB PRG-ROM bank at CPU $8000-$BFFF comprised of selectable high and low banks 16 KiB PRG-ROM bank at CPU $C000-$FFFF comprised of selectable high, fixed low bank bits 1-2 and selectable low bank bit 0 (i.e. low bank register content OR 6)
Banking modes 2 and 3 are rarely used. One multicart that uses them is 4-in-1 (SO1).
Low PRG Bank Register ($4801)
7654 3210 --------- .... .LLL +++- 16 KiB bank number bits 0-2.
Bit 0 is ignored in 32 KiB PRG banking mode.
High PRG Bank Register ($4802)
7654 3210 --------- HHHH HHHH ++++-++++ 16 KiB bank number bits 3-10.
The final 16 KiB PRG-ROM bank number thus is $4801 OR ($4802 SHL 3).
WRAM Bank Register ($4803)
7654 3210 --------- .... ..BB ++ Select 8 KiB WRAM bank at CPU $6000-$7FFF
Apparently some cartridge have an infrared sensor. Infrared receiving is working by having two registers:
$5000-$5FFF: [.... ...V] (read only) V = read current bit from IR sensor $6000-$7FFF: [I... ....] (write only) I = set to activate interrupts by infrared signal
- The commonly-available ROM images of
- 宠物: 小精灵 IV (Chǒngwù: Xiǎo Jīnglíng IV), headerless CRC32 0xB0B13DBD
- Education Computer 32-in-1 (Game Star) [!], headerless CRC32 0xF834F634
- will not work when emulated using the above description. The meaning of registers $4801 and $4802 is swapped, and an emulator must shift the value of $4802 one bit to the left before ORing with $4801. While it cannot be ruled out that these games use an alternative version of the hardware, the more likely explanation is that these are simply bad dumps (notwithstanding GoodNES 3.23b's [!] tag) where the dumper confused the two bank registers.
- Supposedly, the new PRG bank is only committed when $4801 is written. Emulating this supposed behavior however will break Ping Pong, while commiting the PRG bank after any $480x write does not seem to break anything else.
- Most of the educational computers using this mapper require Dendy video timing and will freeze at various points when run with NTSC timing.