Why must data sent from VGA to monitor be at fixed frequencies?

[JohnDoe]

Why some fixed value like 60hz?? Why not 67 or 54? Why not any value just to match "your fav game" engine preferred FPS so that any game or application could run Vsynced without forcing some non-optimal value?

When are we going to see LCD screens capable of actually displaying very high FPS as their response time claim, like a 2ms LCD showing something like 200fps for real? (I didn't cite 500fps for that amount seems unnecessary)



Thank you for caring.

 

[itotallybelieveyou]

Huh? Why do you want 67 FPS specfically? Anymore then 60 isn't really noticable. I mean yes I can tell between 60 and 130-170 but it's difference is minimal

 

[JohnDoe]

67 was just a random number. I want to know why it's necessary to be set at fixed rates, why not any value so a Q3 player could play his game at true 125 fps, or any wierd engine that runs at it's best at 88fps and play such a game with no tearing or whatever glitches at all.

 

[tenaciousleydead]

because you wouldn't be able to see anything more than 60, and the ms refresh time is how fast the screen can go from black to white/colors. thats why you get ghosting on a screen with a high ms refresh

 

[JohnDoe]

Oh cmon people. Cut this "60fps is max for the human eye" , this is just not true. And besides that, that's not the main question. But thanks for caring anyway.

 

[tenaciousleydead]

i know, but its the difference between visible lag and smooth gameplat

 

[itotallybelieveyou]

Oh cmon people. Cut this "60fps is max for the human eye" , this is just not true. And besides that, that's not the main question. But thanks for caring anyway.

THANK YOU SO MUCH!

 

[skittle]

basically it comes down to hardware costs/ compatibility.

 

[altazi]

The vertical refresh rate (frame rate for progressive scan) has to be a sub-multiple of the horizontal refresh (line) rate. As the resolution increases, the number of horizontal lines needed to define a frame increases. So does the pixel frequency, the high-speed clock used to transfer the individual pixel data. Technology and cost issues limit the practical resolution of a video display; todays images are much higher resolution than those 10 years ago.

It is possible to have certain other vertical refresh frequencies, but only with certain other horizontal refresh frequencies. Changing these ratios may cause the video image to be displayed improperly (or not at all). You should be able to select other refresh rates for your video card; why don't you experiment?

Edit: I forgot to mention that the 60Hz frequency was chosen so the refresh rate of a CRT in your TV wouldn't "beat" (create visual interference) against the 60Hz AC line frequency. In the European PAL standard, the vertical refresh rate is 50Hz, to match their AC line frequency. In the "modern" NTSC color television signal, the vertical refresh rate was adjusted to 59.94Hz, so it will be a sub-multiple of the 3.579545MHz color subcarrier.

Regards,

Altazi

 

[poh]

Turn off vsync and if your LCD and video card are up to par you will be able to drive 200 to 500 fps or greater no prob depending on the game/benchmark (with no tearing of frames), not sure I fully get what you are trying to ask. If you are talking about with vsync on, read altazi's post since he nailed it....

 

[caqde]

.... Um ok LCD's Specifically don't need a refresh rate when the LCD screen changes colors it only changes the colors that are needed to be changed hence 60hz and 70hz are the main refresh rates you see for LCD screens.

CRT's on the other hand can go from 60hz to 100hz (at least with mine according to Windows. Mine should be able to go farther though) this is the rate at which the CRT refreshes the screen REDRAWING every pixel. Which is why LCD's don't need that rate they don't redraw every pixel only the ones that need to be changed.

If you want to know more read up about LCD screens. The refresh rate only needs to be high when it is required by the technology driving the hardware.

 

[skittle]

.... Um ok LCD's Specifically don't need a refresh rate when the LCD screen changes colors it only changes the colors that are needed to be changed

This is technically only true for active matrix displays... although i dont think they make too many passive matrix LCDs anymore.

 

[JohnDoe]

The vertical refresh rate (frame rate for progressive scan) has to be a sub-multiple of the horizontal refresh (line) rate. As the resolution increases, the number of horizontal lines needed to define a frame increases. So does the pixel frequency, the high-speed clock used to transfer the individual pixel data. Technology and cost issues limit the practical resolution of a video display; todays images are much higher resolution than those 10 years ago.

It is possible to have certain other vertical refresh frequencies, but only with certain other horizontal refresh frequencies. Changing these ratios may cause the video image to be displayed improperly (or not at all). You should be able to select other refresh rates for your video card; why don't you experiment?

Edit: I forgot to mention that the 60Hz frequency was chosen so the refresh rate of a CRT in your TV wouldn't "beat" (create visual interference) against the 60Hz AC line frequency. In the European PAL standard, the vertical refresh rate is 50Hz, to match their AC line frequency. In the "modern" NTSC color television signal, the vertical refresh rate was adjusted to 59.94Hz, so it will be a sub-multiple of the 3.579545MHz color subcarrier.

Regards,

Altazi

Thanks for your great explanation Altazi. Is that true for LCDs also?

So vertical refresh must be a submultiple of horizontal refresh. And one
can get some non standard vertical refresh values as long as they are some submultiple of hor refresh.

So, the fact that I can't get any hor refresh is a only a tech limit? Puting cost apart, can such a device (that can send data at any rate up to bandwidth limit) be built?


Guys, sure LCDs don't have a refresh the way CRTs do. But VGA certainly send data to them @ fixed rates. And out of Vsync tearing can certainly exist.

 

[altazi]

With CRTs, a horizontal line is drawn by sweeping magnetically-deflected, tightly-focused electron beams from the red, green, and blue electron guns across a phosphor coated surface. This is a little bit simplified, but good enough for "government work". The magnetic deflection signal that creates the horizontal sweep is typically derived from a simple ramping voltage that resets at every HSYNC. The number of pixels per line is a function of how quickly the electron gun drive circuitry can modulate the beam.

In an LCD monitor, the pixels are defined absolutely as row and column positions. This is also a bit simplified, but the video image is shifted, pixel-by-pixel, through the drive electronics and latched by the sync signals. The input is either by analog voltages, in which case the monitor needs to convert them to digital signals internally, or the input is digital to begin with. In either case, a digital clock signal (provided or derived) running at the pixel rate (very high frequency, can be over 100MHz) is used to clock the pixel data into the row drivers.

Edit: The above explanations center on the respective monitor types. The circuitry used to CREATE the video signals must be able to clock data out of graphics memory at rates corresponding to the resolution of the displayed image. FWIW, it is no mean feat to send these high-speed signals over wires.

Additionally, for LCD monitors, if your displayed image is jittering horizontally, this could indicate an improper phase relationship between the video data and the video clock.

Regards,

Altazi

 

[spaztic7]

Newer TVs are starting to go to 120hz.... maybe soon to the monitors?

 

[JohnDoe]

With CRTs, a horizontal line is drawn by sweeping magnetically-deflected, tightly-focused electron beams from the red, green, and blue electron guns across a phosphor coated surface. This is a little bit simplified, but good enough for "government work". The magnetic deflection signal that creates the horizontal sweep is typically derived from a simple ramping voltage that resets at every HSYNC. The number of pixels per line is a function of how quickly the electron gun drive circuitry can modulate the beam.

In an LCD monitor, the pixels are defined absolutely as row and column positions. This is also a bit simplified, but the video image is shifted, pixel-by-pixel, through the drive electronics and latched by the sync signals. The input is either by analog voltages, in which case the monitor needs to convert them to digital signals internally, or the input is digital to begin with. In either case, a digital clock signal (provided or derived) running at the pixel rate (very high frequency, can be over 100MHz) is used to clock the pixel data into the row drivers.

Edit: The above explanations center on the respective monitor types. The circuitry used to CREATE the video signals must be able to clock data out of graphics memory at rates corresponding to the resolution of the displayed image. FWIW, it is no mean feat to send these high-speed signals over wires.

Additionally, for LCD monitors, if your displayed image is jittering horizontally, this could indicate an improper phase relationship between the video data and the video clock.

Regards,

Altazi

Nice answer Altazi. Thanks for responding.

spaztic7

so I hope.