Weird MMC3 board.
Max. 128K PRG ROM.
Max. 64K CHR ROM.
8K CHR RAM.
This is a somewhat odd board- It contains both a 64K CHR ROM, and 8K of CHR RAM too.
A16 selects CHR ROM (0) or CHR RAM (1). The CHR RAM can be banked and mapped like the
CHR ROM, allowing some of the tiles to be software animated, etc. There is a 74HC32 chip
on the board to give the CHR ROM three enables- one for /RD, one for /A13 on the PPU bus,
and one for A16 from the MMC3. This sample is from the game High Speed.