Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!ucselx!bionet!agate!stanford.edu!leland.Stanford.EDU!elaine54.Stanford.EDU!fangchin From: fangchin@elaine54.Stanford.EDU (Chin Fang) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Loop Omnisync non-interlaced monitors (anyone have one?) Message-ID: <1991Apr20.013922.2643@leland.Stanford.EDU> Date: 20 Apr 91 01:39:22 GMT References: <1991Apr17.164509.19165@d.cs.okstate.edu> <1991Apr19.185311.6972@leland.Stanford.EDU> <28109@uflorida.cis.ufl.EDU> Sender: news@leland.Stanford.EDU (Mr News) Organization: Stanford University, California, USA Lines: 120 In article <28109@uflorida.cis.ufl.EDU> jdb@reef.cis.ufl.edu (Brian K. W. Hook) writes: >TIME OUT! > >This discussion has been throwing around the phrase "scan rate" a wee bit >too much. I think we need to start clarifying "horizontal" and "vertical" >since I, for one, am becoming confused. > >Sure, that new Sigma card does 72hZ. But isn't that VSR (vertical scan >rate)? And doesn't that determine flickeriness? A monitor that does 15-48 >is pretty good from what I here. But that is HSR! *NOT* VSR! How can a >monitor that does 48kHz work with a 72kHz card? It WON'T. Why? Because >they are too different ratings! > >Brian > >PS I'm STILL confused! :-) I will just mention a few definitions here: DEFINITION: SCREEN REFRESH RATE = driving clock rate (eg 40Mhz) divided by the product of horizontal frame length and vertical frame length DEFINITION: A horiz frame length is the number of driving clock tics needed for an electron beam to scan the monitor from left to right and back to left. DEFINITION; A vertical frame length is the number of driving clock tics needed for an electron beam to scan the monitor from bottom to top and back to bottom. DEFINITION: horz frame length = driving clock rate (eg 40Mhz) divided by the employed monitor's horizontal sync frequency (eg 60Khz) If you use the max sync rate, you get minimum frame length which is MUST for high refresh rate and thus non-flickering DEFINITION: resolution can be regarded as the portion of frame lengths used for creating viewable image to your eyes. Another way is to say how many pixel (picture elements) on the screen. But people in the know should be able to tell basically I am talking the same thing from different point of views Vertical fame length is often derived using some rules of thumb and I perfer not to elaborate it here. Maybe in a future posting, I will give a more complete explainations to the whole mess. I don't care non-interlaceness. It's a consequence of my derivation. As an example, if you have 1024x728 res. Your horizontal frame length is most likely like 1320 or higher, your vertical frame length is like 820 or so. Therefore, if you use 60Mhz as driving frequency, your screen refresh rate ought to be: 60Mhz/(1320x820)=55.4Hz AND THIS IS POOR!!! You will see flickering at this frequency for sure and that' why I always question people who claim that they can achieve non-flicker 1024x728 using JUST 48Khz horz. Because low horizontal sync means for a given clock, longer frame length. Using the definition of refresh rate that means at this driving clock, you get lower refresh rate and thus flicker! Wisely matched driving clock and monitor sync frequencies is MUST for good quality image. Note, I was talking non-interlace mode above. So now you see, non-interlace ness means nothing without high screen refresh rate. I am going to edit my vedio timing introduction for a PD X server to make it more understandable to MS/DOS or even Mac users as well. As it is now, it has more than eight pages. I want to cut it down to four before I post it. You are not the only one confused. Because I have seen so many misconceptions floating around in this group. And sadly sometimes I even see such from popular mags like PC Mags. Worst, even from Vedio boards' manuals and Monitor makers' manuals. I think it's time to do a once for all post just to get rid of all of such wrong concepts. I started posting only two weeks ago because I couldn't hold myself quiet anymore seeing so many wrong things confusing people. Meanwhile, just remember you need to know four frequencies for your vedio subsystem (including vedio adapter and your monitor) in order of importance: ^^^^^^^^^^^^^^^^^^^^^^ 1. your monitor's maximum horizontal sync rate (perferably high like 60Khz) 2. your vedio board's available driving frequencies (25Mhz, 28Mhz, 32Mhz, 36Mhz, 40Mhz, 45Mhz, 56Mhz, 62Mhz, and 65Mhz. A few good ones even offer driving frequencies higher than 70Mhz, but then you pay $$$ for them. An example is Everex VRAM ViewPoint ET4000 SVGA) Different driving frequencies are for different resolutions. Note, some el cheapo VGA boards may not have all these driving frequencies available. Mostly the higher ones. In that case, you are hosed when you want to run hi-res. 3. your monitor vertical sync rate (greater than 70Hz is highly desirable) 4. your monitor's vedio bandwidth (important to image quality, but most of the time you don't need to worry about this. Most monitors vedio band- width ratings are over kill) To elaborate how they related to each other, I need more than a few paragraphs to make it understandable to high school students. (I am not kidding, I think the basics of vedio timing is so simple that high school kids should under- stand them without much difficulty) Also remember one thing, if you see flicker, don't blame your hardwares first. Most of the time it's poorly written drivers that are culprits. Programmers of these drivers, for marketing/ecomonic reasons, don't not write them smart enough to take advantage your hardware's true potential. This is particularly true in MS/DOS arena. I suffered my share mightly already. Hope your confusion is partially gone by now. Have a happy weekend and happy computing. Chin Fang Mechanical Engineering Department Stanford University fangchin@leland.stanford.edu