Clock rate
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The clock rate of various components in the NES differs between consoles in the USA and Europe due to the different television standards used. The main differences between the NTSC and PAL PPUs are as follows:
| Property | NTSC | PAL |
|---|---|---|
| Master clock speed | 21.477272 MHz ± 40 Hz 236.25 MHz / 11 by definition |
26601712 Hz ± ? 26601712.5 MHz by definition |
| PPU clock speed | 21.477272 MHz / 4 | 26.601712 MHz / 5 |
| Corresponding CPU clock speed | 21.47MHz / 12 = 1.78977267 MHz 3 dots per CPU cycle |
26.601712 MHz /16 = 1.662607 MHz 3 1/5 dots per CPU cycle |
| Height of picture | 240 scanlines | 240 scanlines |
| Nominal visible picture height (see Overscan) |
224 scanlines | 268 scanlines |
| Length of VBLANK | 20 scanlines | 70 scanlines |
| Total number of dots per frame | 341*261 + 340.5 = 89341.5 (scanline 261 is one dot shorter in every other frame) |
341*312 = 106392 |
| Vertical scan rate | 60.0988 Hz | 50.0070 Hz |
Other than these differences and color encoding, the NTSC and PAL PPUs function exactly the same.
