MMC3 with CHR ROM and CHR RAM

MMC3 with CHR ROM and CHR RAM is an uncommon combination.

Apart from Pinbot and High Speed, which use the TQROM board, this combination is used for games in the Chinese language using an MMC3-clone mapper, which need to mix logographic characters arbitrarily. They are thought to follow a similar strategy to Faxanadu and Super Bat Puncher, reserving some CHR RAM for software-rendered text boxes. No mapper other than MMC5 has CHR ROM banks fine-grained enough to allow showing dialogue using Chinese characters with only CHR ROM without prerendering each sentence, and unlike Japanese, Chinese cannot use the common shortcut of using only phonetic characters. Some of these mappers differ only in the amount of CHR RAM that replaces CHR ROM.

All MMC3-like iNES mappers known to be used with CHR RAM are listed below:

Mapper	First RAM bank	Size of RAM (1024-byte banks)	RAM mirrored?
004	0	0 or 8*	Yes
074	8	2	No
119	64, 192	8	Yes
176	0	8	No
191	128	2	Yes
192	8	4	No
194	0	2	No
195	0	4	No

* In iNES format, mapper 4 has CHR RAM only if CHR ROM is not present.

ROMs with the NES 2.0 header specify the size of CHR RAM separately. Because the default size is ignored, the seven mappers collapse into four distinct behaviors:

004, 194, 195

CHR RAM starts at bank 0 and is mirrored only if there is no CHR ROM

074, 192

CHR RAM starts at bank 8 and is not mirrored

119

CHR A16 switches between CHR ROM and CHR RAM

176

$A001 bit 2 switches between CHR ROM and CHR RAM in the first 8 KiB

191

CHR A17 switches between CHR ROM and CHR RAM