ttp://nesdev.com/2C02%20technical%20reference.TXT - palette RAM is accessed internally during playfield rendering (i.e., the palette address/data is never put on the PPU bus during this time).
しかしこういう挙動もある、これはレンダリング止めた場合だろう？ Additionally, when the programmer accesses palette RAM via $2006/7, the palette address accessed actually does show up on the PPU address bus, but the PPU's /RD & /WR flags are not activated. この辺あやしいね
