NES 2.0 Mapper 497

NES 2.0 Mapper 497 denotes the 小霸王 (Xiǎobàwáng, a.k.a. Subor) LOGO cartridge's circuit board.

Banks

• CPU $8000-$FFFF: 32 KiB unbanked PRG-ROM
• PPU $0000-$0FFF: 4 KiB PRG-RAM window into 32 KiB of CHR-RAM, fixed at bank #0
• PPU $1000-$1FFF: 4 KiB PRG-RAM window into 32 KiB of CHR-RAM, switchable

Register

CHR-RAM Bankswitching Mode

D~[.... ..BA] A~[1... .... .... ....] ($8000-$FFFF, no bus conflicts)
          ++- PPU $1000-$1FFF bank
               0,1: set to bank #1
               2:   automatically switch to PPU A9..8 latched at rising edge of PPU A13, +2
               3:   like 2, but when PPU A9..8 is 3, set to bank #1

Effective CHR-RAM banks

PPU $1000-$1FFF switching mode	Last nametable fetch address (excluding attribute table fetches)	4 KiB CHR-RAM bank at PPU $0000	4 KiB CHR-RAM bank at PPU $1000
0	-	0	1
1	-	0	1
2	0xx	0	2
2	1xx	0	3
2	2xx	0	4
2	3xx	0	5
3	0xx	0	2
3	1xx	0	3
3	2xx	0	4
3	3xx	0	1

Mode 3 is used to facilitate a split screen with graphics on top and text in the bottom six character rows.