ROM Nametables are active while the PPU is reading if:
- Extended Mirroring is active ($D000 bit $20s or $D001 bit $08s set) and not suppressed via Jumper (i.e. not Mapper 90), and
- enabled for all nametables if $D000 bit $40s is set, or for each nametable individually if that nametable 's $B00x bit $80s is the opposite of $D002 bit $80s.
ROM nametables not being active during PPU writes is relevant for the game Tiny Toon Adventures 6 (original Mapper 211 version): if ROM nametables are active during writing, the initial text in the introduction ("Baabs is dreaming about becoming an actress. She is daydreaming that she has great courage, intelligence and power") will not be shown even as the letter printing sound effect is heard, and the text window will remain blank during those lines. Only BizHawk gets it right, Nestopia, FCEUX, puNES, Mesen and stock Nintendulator get it wrong, and RockNES does not support Mapper 211.