Questions and Answers

# 10 Questions and Answers

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Q. The example you gave is not a standard screen size, can I use it?

A. Why not? There is NO reason whatsoever why you have to use 640x480, 800x600, or even 1024x768. XFree86 driver lets you config your hardware with a lot of freedom. It usually takes two to three minutes to come up the right one. The important thing to shoot for is high refresh rate with reasonable viewing area. not high resolution at the price of eye-tearing flicker!

Q. It this the *only* resolution given the 65Mhz dot clock and 55Khz HSF?

A. Absolutely not! You are encouraged to follow the general procedure and do some trial-and-error to come up with a setting that's really to your liking. Experimenting with this can be lots of fun. Most settings may just give you nasty video hash, but nothing you do can actually damage a multi-sync monitor (unless you somehow force your card to clock it at way above its bandwidth --- if you stick reasonably close to the highest resolution the monitor is documented to support this can't happen). Beware fixed-frequency monitors! This kind of hacking around *can* damage them.

Q. You just mentioned two standard resolutions. In Xconfig, there are many standard resolutions available, can you tell me whether there's any point in tinkering with timings?

A. Absolutely! Take, for example, the "standard" 640x480 listed in the current Xconfig. It employs 25Mhz driving frequency, frame lengths are 800 and 525 => refresh rate ~ 59.5Hz. Not too bad. But 28Mhz is a commonly available driving frequency from many SVGA boards. If we use it to drive 640x480, following the procedure we discussed above, you would get frame lengths like 812 and 505. Now the refresh rate is raised to 68Hz, a quite significant improvement over the standard one.

Q. But how about interlace/non-interlace?

A. At a fixed dot clock, an interlaced display is going to flicker worse than a non-interlaced one, which is why the market has moved away from them. What you buy with the increased flicker is higher resolution with a slower dot clock. If the DCF were fast enough (say 90MHz or up) even interlacing wouldn't produce flicker -- but at present speeds, interlaced monitors are a bad idea for X.

Q. Can you summarize what we have discussed so far?

A. In a nutshell:

1. for any fixed driving frequency, raising max resolution incurs the penalty of lowering refresh rate and thus introducing more flicker.
2. if high resolution is desirable and your monitor supports it, try to get a SVGA card that provides a matching dot clock or DCF. The higher, the better!

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