|
|
| (39 intermediate revisions by 4 users not shown) |
| Line 1: |
Line 1: |
| 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.
| |
| So the main differences between the NTSC and PAL PPUs are as follows:
| |
| {| class="tabular"
| |
| ! Property || NTSC || PAL || Dendy
| |
| |-
| |
| | 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
| |
| |-
| |
| | 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>3⅕ dots per CPU cycle || 26.601712 MHz ÷ 15 = 1.773448 MHz<br>3 dots per CPU cycle
| |
| |-
| |
| | Height of picture || 240 scanlines || 240 scanlines || Like PAL
| |
| |-
| |
| | Nominal visible picture height<br>(see [[Overscan]]) || 224 scanlines || 268 scanlines || Like PAL
| |
| |-
| |
| | "Post-render" blanking lines between end of picture and NMI || 1 scanline || 1 scanline || 51 scanlines
| |
| |-
| |
| | Length of vertical blanking after NMI || 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<br>(pre-render line 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.
| |
| | |
| 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.
| |
| | |
| [[wikipedia:Dendy (console)|Dendy]] is a clone of the Famicom distributed by Steepler and sold in Russia.
| |
| 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.
| |
| 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'').
| |
| This explains the faster CPU divider and longer post-render period vs. the authentic PAL NES.
| |
| | |
| To compensate for these speed differences, you can [[detect TV system|detect the TV system]] at power-on.
| |
