Dot clock rates
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 that each rate produces, assuming the 480-line picture and 52.148 microsecond active scanline period of Rec. 601, is also given.
A few things may cause this ratio to differ in a particular environment:
- Some coin-operated machines use a different active scanline period, and the arcade operator is expected to adjust the monitor's picture size to match a test pattern displayed in a particular game's service mode. An arcade-to-television adapter would produce the pixel aspect ratio listed below.
- Some devices also support 480i (interlaced) video, where even scanlines are drawn in one field and odd scanlines are drawn in the other field. Interlaced video makes pixels half as tall as in 240p, doubling the pixel aspect ratio, and ratios assuming interlace are marked as such.
- 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|
|4.61 MHz||576/125 MHz||1.33||1875:1408||Konami GX400 family (a.k.a. Nemesis and Bubble System) (256px)|
|5.00 MHz||5/1 MHz||1.22||27:22||Atari Missile Command and Crystal Castles hardware, Stern Berzerk/Frenzy hardware (all 256px)|
|5.37 MHz||945/176 MHz||1.14||8:7||The 256px display of the TMS9918 (TI-99/4A, ColecoVision, MSX, and SG-1000), its descendants (MSX2, Master System, Genesis, Game Gear), and other VDPs inspired by it (NES, TurboGrafx-16, Super NES), and 256px mode of the original PlayStation|
|5.59 MHz||16777216/3 Hz||1.10||6328125:5767168||Nintendo DS (256px) is the ~33.5 MHz (apparently 225 Hz) master clock divided by 6|
|6.00 MHz||6/1 MHz||1.02||45:44|| Data East Lock'n Chase/BurgerTime family (240 or 256px), DECO Cassette System (256px), and BreakThru family (240px)|
Technos Double Dragon hardware, SNK pre-Neo Geo 68000-based hardware, Taito Arkanoid and Bubble Bobble hardware, Jaleco Mega System 1-A (all 256px)
Konami GX and pre-GX (Mystic Warriors) family (288px)
Neo Geo MVS (320px)
|6.04 MHz||6048/1001 MHz||1.02||65:64||Neo Geo AES (320px)|
|6.05 MHz||756/125 MHz||1.01||625:616||Namco NB-1/NB-2 family (288px)|
|6.09 MHz||1071/176 MHz||1.01||120:119||Nintendo 64 (320px)|
|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|
|6.14 MHz||768/125 MHz||1.00||5625:5632|| 48000 kHz (DAT and DVD audio rate) * 128 approximates square pixels to within 1 part in 800|
Irem M52 (Moon Patrol) (240px)
Namco Pac-Man/Galaxian hardware and derivatives such as Pengo (288px)
Namco Super Pac-Man family, System 86, 1, 2, and ND-1 (all 288px)
|6.25 MHz||25/4 MHz||0.98||54:55||Sega X-Board (320px)|
|6.29 MHz||900/143 MHz||0.975||39:40|| Sega Hang-On/Space Harrier, OutRun, and System 16B hardware (all 320px) divide a VGA crystal by 4.|
Mode X (320x240) on VGA has twice the dot rate and repeats each line twice, giving it the same PAR.
|6.71 MHz||4725/704 MHz||0.91||32:35||Sega Genesis and PlayStation 320px mode, very close to SIF|
|6.75 MHz||27/4 MHz||0.91||10:11|| MPEG-1 NTSC SIF (352 or 360px): CD-i, Video CD. Equal to Rec. 601 chroma rate or half Rec. 601 luma rate.|
Toaplan/Raizing 2nd-generation arcade boards (320px)
|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|
|7.00 MHz||7/1 MHz||0.88||135:154||Toaplan/Taito Wardner hardware, Toaplan "1st generation" hardware, Technos Double Dragon 3 family (all 320px)|
|7.16 MHz||315/44 MHz||0.86||6:7||Apple II (40-column text, HGR 280px); TG16 (mid-res, up to 352px); Atari 7800 (hi-res, 320px); Amiga, IBM CGA (40-column or 320px) and EGA in 200-line mode (40-column or 320px); Atari 800; Tandy Color Computer (COCO) and other computers using Motorola 6847 video chip; Atari Tetris and Klax arcade games (336px)|
|7.67 MHz||4725/616 MHz||0.8||4:5||PlayStation (366px)|
|8.00 MHz||8/1 MHz||0.77||135:176|| Williams 6809-based arcade system (276, 292, or 316px)|
Capcom CP System and CP System II (384px)
|8.19 MHz||630/77 MHz||0.75||3:4||Commodore 64 and Apple IIGS 4bpp super hi-res (both 320px). Square on widescreen monitors.|
|10.74 MHz||945/88 MHz||0.57||4:7||Twice the TMS9918 pixel rate produces 512px on Super NES, TG16, and PlayStation|
|12.27 MHz||135/11 MHz||1.00 (i)||1:1 (i)||Square interlaced pixels|
|13.42 MHz||4725/352 MHz||0.46||16:35||PlayStation (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 (704px)|
|14.32 MHz||315/22 MHz||0.43||3:7||Apple II (80-column text, double hi-res); Amiga; IBM CGA (80-column)|
|16.36 MHz||1260/77 MHz||0.375||3:8||Apple IIGS 2bpp super hi-res (640px) though Apple has claimed 5:12 instead|
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 mode 12h (640x480). The horizontal scan rate is twice NTSC, and the dot clock is 800 times that: 640 dots of picture and 160 of blanking.|
|27.00 MHz||27/1 MHz||0.91||10:11|| Twice Rec. 601 luma rate, as produced by progressive scan DVD players (704px)|
- nemesis.cpp from MAME; this information had been included in the MAME driver code as an arithmetic calculation long before the modern
set_rawfunction was called
- missile.cpp from MAME
- ccastles.cpp from MAME
- berzerk.cpp from MAME
- Game Gear divides a 32.2159 MHz crystal by 6 to produce the dot clock. This frequency is 9 times NTSC color burst, and each RGB pixel is 6 dots, divided into three 2-dot subpixels. Evil Tim's SCART mod produces 240p RGB output centered in the screen with the same size as a Super Game Boy picture.
- HuC6260 - Archaic Pixels
- The PS1 divides a 15 times NTSC (53.69 MHz) crystal by 10, 8, 7, 5, or 4 Post by Ryphecha on Mednafen forum
- GBATEK by Martin Korth
- btime.cpp from MAME
- decocass.cpp from MAME
- brkthru.cpp from MAME
- ddragon.cpp from MAME
- snk68.cpp from MAME
- arkanoid.cpp from MAME
- bublbobl.cpp from MAME
- megasys1.cpp from MAME. The same pixel clock is possible but unverified for the other Mega System 1 variants.
- konamigx.cpp from MAME
- mystwarr.cpp from MAME
- video/neogeo_spr.h from MAME. Many Neo Geo games are designed around a safe area approximately 304 pixels wide.
- 384 pixels per standard 227.5-cycle scanline period. See NESdev posts by TmEE and psycopathicteen. TODO: Verify whether the timing differences from MVS are noted anywhere in the MAME source code.
- namconb1.cpp from MAME: same divisor and dot counts that originated from Galaxian, except with a slower crystal (48.384MHz)
- assemblergames forum post
- MX8350 clock generator
- includes/n64.h from MAME. Note the mention of quarter-pixel scanline length in n64.cpp; divide the given
DACRATE_NTSCby 8 to obtain the result here.
- Wikipedia:Crystal oscillator frequencies
- m52.cpp from MAME
- pacman.cpp from MAME
- video/galaxian.cpp from MAME. The "6MHz" mentioned in some comments is only an approximation.
- pengo.cpp from MAME
- mappy.cpp from MAME
- namcos86.cpp from MAME
- namcos1.cpp from MAME
- namcos2.cpp from MAME
- namcond1.cpp from MAME
- segaxbd.cpp from MAME
- MAME segahang.cpp
- MAME segaorun.cpp
- MAME segas16b.cpp. Look carefully at how
MASTER_CLOCK_25MHzis defined. System 16A contains the same crystal according to comments in xtal.h, but its use is not yet noted in segas16a.cpp.
- kyuusaku reasons from the 15*CB oscillator
- toaplan2.cpp from MAME
- wardner.cpp from MAME
- toaplan1.cpp from MAME
- ddragon3.cpp from MAME
- reenigne. "VGA 15kHz Output". 2014-01-18. Accessed 2016-01-26.
- phaeron's post
- The 6847 is clocked at the NTSC color burst frequency. Its datasheet lists the left and right border widths as 29.5 and 28 cycles on p. 5, and subtracting those from the 186+2/3 cycles of a standard scanline leaves just over 131 cycles of active picture. In addition, tDOT on p. 7 appears to be half a color burst cycle. Furthermore, the width of low and high phases of the clock "controls the width of alternate dots on the television screen" (p. 13).
- atetris.cpp and klax.cpp from MAME
- williams.cpp from MAME
- includes/cps1.h from MAME. For comparison, Irem's M72 family (m72.cpp) and Konami's Xexex (xexex.cpp) also use a 384px-wide clean aperture and an 8MHz dot clock, but they have slower-than-NTSC frame rates of about 54–55 Hz.
- Post by Michael J. Mahon to comp.sys.apple2
- "Nintendo GameCube Digital AV Connector". NFG Games + GameSX. Accessed 2016-04-02.
- Apple IIGS Tech Note #41: Font Family Numbers
- Wikipedia:Video Graphics Array. Accessed 2013-09-24.