Difference between revisions of "Dot clock rates"

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m (clarify last edit)
(I'd guess the Sega System 16B crystal is a VGA crystal. The VGA frequency is supposed to be 800 times the 480p horizontal scan rate: 3600/143 = 25.1748 MHz. Got a cite for System 16B?)
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| 6.00 MHz || 6 MHz || 1.02 || 45:44 || Neo Geo
 
| 6.00 MHz || 6 MHz || 1.02 || 45:44 || Neo Geo
 
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| 6.14 MHz || 135/22 MHz || 1.00 || 1:1 || Rec. 601 defines the NTSC picture such that this is square on 4:3 monitors.
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| 6.14 MHz || 135/22 MHz || 1.00 || 1:1 || Rec. 601 defines the NTSC picture such that this is square on 4:3 monitors
 
|-
 
|-
 
| 6.25 MHz || 25/4 MHz || 0.98 || 54:55 || Nintendo 64 (320px)<ref>[http://nfggames.com/forum2/index.php?topic=1722.0;wap2 N64 DENC RGB]</ref>
 
| 6.25 MHz || 25/4 MHz || 0.98 || 54:55 || Nintendo 64 (320px)<ref>[http://nfggames.com/forum2/index.php?topic=1722.0;wap2 N64 DENC RGB]</ref>
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| 14.32 MHz || 315/22 MHz || 0.43 || 3:7 || Apple II (80-column text, double hi-res); Amiga; IBM CGA (80-column)<ref name="towcrystals" />
 
| 14.32 MHz || 315/22 MHz || 0.43 || 3:7 || Apple II (80-column text, double hi-res); Amiga; IBM CGA (80-column)<ref name="towcrystals" />
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|}
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For comparison, here are some enhanced-definition (480p) rates, with a horizontal scan frequency close to 31.5 kHz:
 +
{| class="tabular"
 +
! Frequency || Exact frequency || PAR || Exact PAR || Devices
 +
|-
 +
| 25.17 MHz || 3600/143 MHz || 0.975 || 39:40 || VGA (640x480). The horizontal scan rate is twice NTSC, and the dot clock is 800 times that: 640 dots of picture and 160 of blanking.<ref name="towvga">[[Wikipedia:Video Graphics Array]]. Accessed 2013-09-24.</ref>
 
|}
 
|}
  
 
== References ==
 
== References ==
 
<references />
 
<references />

Revision as of 20:15, 24 September 2013

The following frequencies are the dot clock rates of digital picture generators outputting 240p low-definition video signals that are compatible with NTSC monitors or otherwise at near-System M scan rates (15.7 kHz horizontal, 60 Hz vertical). The pixel aspect ratio, assuming the 480-line picture and 52.148 microsecond active scanline period of Rec. 601, are also given. Some devices also supported 480i (interlaced) video, where even scanlines are drawn in one field and odd scanlines are drawn in the other field; these have double the pixel aspect ratio. Sets of the 240p era were built for 4:3 display aspect ratio, as opposed to the 16:9 aspect ratio that became common between the late 1990s and mid-2000s; multiply the pixel aspect ratios by 4/3 if stretching the picture on a widescreen TV.

Frequency Exact frequency PAR Exact PAR Devices
1.02 MHz 315/308 MHz 1.50 3:2 Apple II (GR; each line repeated four times)
3.58 MHz 315/88 MHz 1.71 12:7 Devices with 1 pixel per NTSC subcarrier period: Atari 2600, Atari 7800, Intellivision
5.00 MHz 5 MHz 1.22 27:22 Missile Command hardware[1]
5.37 MHz 945/176 MHz 1.14 8:7 Anything descended from a TMS9918 (ColecoVision, MSX, SG-1000, Master System, Genesis 256px) or inspired by it (NES, TurboGrafx-16,[2] Super NES)
6.00 MHz 6 MHz 1.02 45:44 Neo Geo
6.14 MHz 135/22 MHz 1.00 1:1 Rec. 601 defines the NTSC picture such that this is square on 4:3 monitors
6.25 MHz 25/4 MHz 0.98 54:55 Nintendo 64 (320px)[3]
6.71 MHz 4725/704 MHz 0.91 32:35 Sega Genesis and PlayStation 320px mode,[4] very close to SIF
6.75 MHz 27/4 MHz 0.91 10:11 MPEG-1 NTSC SIF: CD-i, Video CD. Equal to Rec. 601 chroma rate or half Rec. 601 luma rate.
6.75 MHz 27/4 MHz 1.82 (i) 20:11 (i) Low-resolution DVD Video, such as that produced by DVD recorders in long play mode
7.16 MHz 315/44 MHz 0.86 6:7 Apple II (40-column text, HGR); TG16 (mid-res); Atari 7800 (hi-res); Amiga, IBM CGA (40-column) [5]
7.50 MHz 15/2 MHz 0.82 9:11 Capcom CPS3[6]
8.00 MHz 8 MHz 0.77 135:176 Capcom CPS1 and CPS2[7]
8.19 MHz 630/77 MHz 0.75 3:4 Commodore 64. Square on widescreen monitors.
10.74 MHz 945/88 MHz 0.57 4:7 Super NES and TG16 (hi-res)
12.27 MHz 135/11 MHz 1.00 (i) 1:1 (i) Square interlaced pixels
12.50 MHz 25/2 MHz 0.49 27:55 Nintendo 64 (640px)
13.50 MHz 27/2 MHz 0.91 (i) 10:11 (i) Rec. 601 luma rate as used in D1 tape and DVD Video
14.32 MHz 315/22 MHz 0.43 3:7 Apple II (80-column text, double hi-res); Amiga; IBM CGA (80-column)[5]

For comparison, here are some enhanced-definition (480p) rates, with a horizontal scan frequency close to 31.5 kHz:

Frequency Exact frequency PAR Exact PAR Devices
25.17 MHz 3600/143 MHz 0.975 39:40 VGA (640x480). The horizontal scan rate is twice NTSC, and the dot clock is 800 times that: 640 dots of picture and 160 of blanking.[8]

References