以下 NTSC 2C02 technical reference から抜粋 > Other than the 3-stage Johnson counter, the 21.48 MHz signal is not used > directly by any other PPU hardware. Instead, the signal is divided by 4 to >get 5.37 MHz, and is used as the smallest unit of timing in the PPU.
> - 341 PPU cc's make up the time of a typical scanline (or 341/3 CPU cc's). > - One frame consists of 262 scanlines. This equals 341*262 PPU cc's per > frame (divide by 3 for # of CPU cc's).
