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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 (NTSC M vs. PAL B). The color encoding method used by the NES (see [[NTSC video]]) requires that the master clock frequency be six times that of the color subcarrier, but this frequency is about 24% higher on PAL than on NTSC. In addition, PAL has more scanlines per field and fewer fields per second than NTSC.
| | #REDIRECT [[Cycle reference chart]] |
| Furthermore, the PAL CPU's master clock should have been divided by 15 to preserve the ratio between CPU and PPU speeds, but dividing a clock by an odd factor is more complicated despite that Nintendo managed it for the PAL PPU, and so Nintendo chose to divide by 16 instead.
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| So the main differences between the NTSC and PAL PPUs are as follows:
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| {| class="tabular"
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| ! Property || NTSC || PAL || Dendy
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| | Master clock speed || 21.477272 MHz ± 40 Hz<br>236.25 MHz ÷ 11 by definition || 26601712 Hz ± ?<br>26601712.5 Hz by definition || Like PAL
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| |-
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| | PPU clock speed || 21.477272 MHz ÷ 4 || 26.601712 MHz ÷ 5 || Like PAL
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| | Corresponding CPU clock speed || 21.47MHz ÷ 12 = 1.78977267 MHz<br>3 dots per CPU cycle || 26.601712 MHz ÷ 16 = 1.662607 MHz<br>3⅕ dots per CPU cycle || 26.601712 MHz ÷ 15 = 1.773448 MHz<br>3 dots per CPU cycle
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| | Height of picture || 240 scanlines || 240 scanlines || Like PAL
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| | Nominal visible picture height<br>(see [[Overscan]]) || 224 scanlines || 268 scanlines || Like PAL
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| |-
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| | "Post-render" blanking lines between end of picture and NMI || 1 scanline || 1 scanline || 51 scanlines
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| | Length of vertical blanking after NMI || 20 scanlines || 70 scanlines || 20 scanlines
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| | "Pre-render" lines between vertical blanking and next picture || 1 scanline || 1 scanline || Like PAL
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| | Total number of dots per frame || 341 × 261 + 340.5 = 89341.5<br>(pre-render line is one dot shorter in every other frame) || 341 × 312 = 106392 || Like PAL
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| |-
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| | Vertical scan rate || 60.0988 Hz || 50.0070 Hz || Like PAL
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| |}
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| Other than these differences and color encoding, the NTSC and PAL PPUs function exactly the same.
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| The authentic NES sold in Brazil is an NTSC NES with an adapter board to turn the NTSC video into [[wikipedia:PAL-M|PAL-M video]], a variant of PAL using NTSC frequencies but PAL's color modulation.
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| [[wikipedia:Dendy (console)|Dendy]] is a clone of the Famicom distributed by Steepler and sold in Russia.
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| Because not many people in the English-speaking NESdev community have a Dendy, its precise differences from the authentic Nintendo hardware are not completely understood, and the values above are partly conjecture.
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| But it is known that the chipset in Dendy and several other PAL famiclones is designed for compatibility with Famicom games, including games with CPU cycle counting mappers (e.g. [[VRC4]]) and games that use a cycle-timed NMI handler (e.g. ''Balloon Fight'').
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| This explains the faster CPU divider and longer post-render period vs. the authentic PAL NES.
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| To compensate for these speed differences, you can [[detect TV system|detect the TV system]] at power-on.
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