Clock rate: Difference between revisions
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m (moved PPU ntsc pal difference to Clock rate: What actually differs between the two systems) |
(In Russia, dendy plays YOU) |
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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: | 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: | ||
{| border=1 | {| border=1 | ||
! Property || NTSC || PAL | ! Property || NTSC || PAL || Dendy | ||
|- | |- | ||
| Master clock speed || 21.477272 MHz ± 40 Hz<br>236.25 MHz / 11 by definition || 26601712 Hz ± ?<br>26601712.5 MHz by definition | | Master clock speed || 21.477272 MHz ± 40 Hz<br>236.25 MHz / 11 by definition || 26601712 Hz ± ?<br>26601712.5 MHz by definition || Like PAL | ||
|- | |- | ||
| PPU clock speed || 21.477272 MHz / 4 || 26.601712 MHz / 5 | | PPU clock speed || 21.477272 MHz / 4 || 26.601712 MHz / 5 || Like PAL | ||
|- | |- | ||
| Corresponding CPU clock speed || 21.47MHz / 12 = 1.78977267 MHz<br>3 dots per CPU cycle || 26.601712 MHz /16 = 1.662607 MHz<br>3 1/5 dots per CPU cycle | | Corresponding CPU clock speed || 21.47MHz / 12 = 1.78977267 MHz<br>3 dots per CPU cycle || 26.601712 MHz / 16 = 1.662607 MHz<br>3 1/5 dots per CPU cycle || 26.601712 MHz / 15 = 1.773448 MHz<br>3 dots per CPU cycle | ||
|- | |- | ||
| Height of picture || 240 scanlines || 240 scanlines | | Height of picture || 240 scanlines || 240 scanlines || Like PAL | ||
|- | |- | ||
| Nominal visible picture height<br>(see [[Overscan]]) || 224 scanlines || 268 scanlines | | Nominal visible picture height<br>(see [[Overscan]]) || 224 scanlines || 268 scanlines || Like PAL | ||
|- | |- | ||
| | | "Post-render" lines between vertical blanking and picture || 1 scanline || 1 scanline || 51 scanlines | ||
|- | |- | ||
| | | Length of vertical blanking || 20 scanlines || 70 scanlines || 20 scanlines | ||
|- | |- | ||
| Vertical scan rate || 60.0988 Hz || 50.0070 Hz | | "Pre-render" lines between vertical blanking and next picture || 1 scanline || 1 scanline || Like PAL | ||
|- | |||
| Total number of dots per frame || 341*261 + 340.5 = 89341.5<br>(scanline 261 is one dot shorter in every other frame) || 341*312 = 106392 || Like PAL | |||
|- | |||
| Vertical scan rate || 60.0988 Hz || 50.0070 Hz || Like PAL | |||
|} | |} | ||
Other than these differences and color encoding, the NTSC and PAL PPUs function exactly the same. | Other than these differences and color encoding, the NTSC and PAL PPUs function exactly the same. | ||
[[wikipedia:Dendy (console)|Dendy]] is a clone of the Famicom made by Steepler and sold in Russia. | |||
Because not many people in the English-speaking have a Dendy, its precise differences from the authentic Nintendo hardware are not completely understood. | |||
But it is known that the Dendy is designed for compatibility with Famicom games, including games with CPU cycle counting mappers and games that use a cycle-timed NMI handler. | |||
This explains the faster CPU divider and longer post-render period vs. the authentic PAL NES. | |||
Revision as of 19:16, 7 April 2010
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 | Dendy |
|---|---|---|---|
| Master clock speed | 21.477272 MHz ± 40 Hz 236.25 MHz / 11 by definition |
26601712 Hz ± ? 26601712.5 MHz by definition |
Like PAL |
| PPU clock speed | 21.477272 MHz / 4 | 26.601712 MHz / 5 | Like PAL |
| 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 |
26.601712 MHz / 15 = 1.773448 MHz 3 dots per CPU cycle |
| Height of picture | 240 scanlines | 240 scanlines | Like PAL |
| Nominal visible picture height (see Overscan) |
224 scanlines | 268 scanlines | Like PAL |
| "Post-render" lines between vertical blanking and picture | 1 scanline | 1 scanline | 51 scanlines |
| Length of vertical blanking | 20 scanlines | 70 scanlines | 20 scanlines |
| "Pre-render" lines between vertical blanking and next picture | 1 scanline | 1 scanline | Like PAL |
| 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 | Like PAL |
| Vertical scan rate | 60.0988 Hz | 50.0070 Hz | Like PAL |
Other than these differences and color encoding, the NTSC and PAL PPUs function exactly the same.
Dendy is a clone of the Famicom made by Steepler and sold in Russia. Because not many people in the English-speaking have a Dendy, its precise differences from the authentic Nintendo hardware are not completely understood. But it is known that the Dendy is designed for compatibility with Famicom games, including games with CPU cycle counting mappers and games that use a cycle-timed NMI handler. This explains the faster CPU divider and longer post-render period vs. the authentic PAL NES.
