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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 could have been divided by 15 to preserve the ratio between CPU and PPU speeds, but Nintendo chose to keep the [[wikipedia:Ring counter|Johnson counter]] structure, which always has an even period, and divide by 16 instead.
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| So the main differences between the NTSC and PAL PPUs are depicted in the below chart:
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| {| class="tabular"
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| ! Property
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| ! NTSC (2C02)
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| ! PAL (2C07)
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| ! Dendy
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| ! RGB (2C03)
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| ! RGB (2C04)
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| ! RGB (2C05)
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| |-
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| | Master clock speed
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| | 21.477272 MHz ± 40 Hz<br/>236.25 MHz ÷ 11 by definition
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| | 26601712 Hz ± ?<br/>26601712.5 Hz by definition
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| | Like PAL
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| | colspan=3 align=center|Like NTSC
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| |-
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| | PPU clock speed
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| | 21.477272 MHz ÷ 4
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| | 26.601712 MHz ÷ 5
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| | Like PAL
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| | colspan=3 align=center|Like NTSC
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| |-
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| | Corresponding CPU clock speed
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| | 21.47 MHz ÷ 12 = 1.789773 MHz<br/>3 dots per CPU cycle<br/>Same as NTSC Amiga clock ÷ 4
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| | 26.60 MHz ÷ 16 = 1.662607 MHz<br/>3⅕ dots per CPU cycle
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| | 26.60 MHz ÷ 15 = 1.773448 MHz<br/>3 dots per CPU cycle<br/>Same as PAL Amiga clock ÷ 4
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| | colspan=3 align=center|Like NTSC
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| |-
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| | Height of picture
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| | colspan="6" align="center" | 240 scanlines
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| |-
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| | Nominal visible picture height (see [[Overscan]])
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| | 224 scanlines
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| | 268 scanlines
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| | Like PAL
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| | colspan=3 align=center|Like NTSC
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| |-
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| | "Post-render" blanking lines between end of picture and [[NMI]]
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| | 1 scanline
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| | 1 scanline
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| | 51 scanlines
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| | colspan=3 align=center|Like NTSC
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| |-
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| | Length of vertical blanking after NMI
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| | 20 scanlines
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| | 70 scanlines
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| | 20 scanlines
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| | colspan=3 align=center|Like NTSC
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| |-
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| | Time during which [[OAM]] can be written
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| | Vertical or forced blanking
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| | Only during first 20 scanlines after NMI
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| | Like NTSC
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| | colspan=3 align=center|Like NTSC
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| |-
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| | "Pre-render" lines between vertical blanking and next picture
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| | colspan="6" align="center" | 1 scanline
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| |-
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| | Total number of dots per frame
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| | 341 × 261 + 340.5 = 89341.5<br/>(pre-render line is one dot shorter in every other frame)
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| | 341 × 312 = 106392
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| | Like PAL
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| | colspan=3 align=center| 341 × 262 = 89342
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| |-
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| | Vertical scan rate
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| | 60.0988 Hz
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| | 50.0070 Hz
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| | Like PAL
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| | colspan=3 align=center|60.0985 Hz
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| |-
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| | Color of top and bottom borders
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| | N/A
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| | Always black ($1D)
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| | Like PAL
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| | ?
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| | ?
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| | ?
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| |-
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| | Side borders
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| | [[PPU_palettes|Palette]] entry at $3F00
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| | Always black ($1D), intruding on left and right 2 pixels of picture
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| | Like PAL
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| | ?
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| | ?
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| | ?
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| |-
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| | Color emphasis<br/>(with correlating bit in [[PPUMASK]])
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| | Blue (D7), green (D6), red (D5)
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| | Blue (D7), red (D6), green (D5)
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| | Like PAL
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| | colspan=3 align=center|Blue, green, red (full scale)
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| |-
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| | Other quirks
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| | Missing $2D and $3D greys
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| | Permutated palette
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| | [[PPUCTRL]] and [[PPUMASK]] are swapped; revision ID in [[PPUSTATUS]] (D4-D0)
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| |}
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| The 2C03, 2C04, and 2C05 PPUs were all found in Nintendo's [[wikipedia:Nintendo_VS._System|Vs. System]] and [[wikipedia:PlayChoice-10|PlayChoice-10]] (a.k.a. PC10 or PC-10) arcade systems.
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| Famicom Titler, Famicom TVs, and RGB-modded NES consoles would use either the 2C03 or a 2C05 with glue logic to unswap $2000 and $2001.
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| (Later RGB mods used a 2C02 in output mode and faked out all palette logic.)
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| The color emphasis bits on the PAL NES have their red and green bits swapped.
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| http://wiki.nesdev.org/w/index.php/PPU_registers#Mask_.28.242001.29_.3E_write
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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 differences, you can [[detect TV system|detect the TV system]] at power-on.
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