Re: How to calculate the proper modeline? (DCF?

[Oleg Krivosheev <kriol@fnal.gov>]

Hi,

   *-Jan Krupa <krupa@alpha.sggw.waw.pl>
   |
   | I am reading "XFree86 Video Timings HOWTO" and I would like to
   | compute DCF/HSF but I do not know what DCF (dot clock frequency)
   | is ? I mean I do not know where it comes from?

   It's the number of pixels that the video card will send to the
   monitor each second. Both the card and monitor must be able to
   handle the DCF.

   If you keep the resolution fixed and increase the dotclock the
   monitor will refresh the image more often. If you keep the
   refresh rate fixed and increase the dotclock, the resolution
   will be greater.

   | Synchronization :Horizontal: 30KHz-70KHz (Automatically)
   |                 :Vertical: 50Hz-160Hz (Automatically)
   | 
   | Video Bandwidth  : 100MHz at-3db

   This is the biggest dotclock that the monitor can handle without
   much problem. 

well, that's not true. The number mentioned is so-called "typical"
bandwidth. You should be able 1280x1024x66Hz at approx 120MHz
or 1152x864x78Hz at approx 110MHz (that's what i'm running now
having about the same monitor, feel free to ask config)

   It's not a fixed number, meaning that if you are
   desperate, you can push it a little (but don't blame me if anything
   goes wrong).

AFAIK, if you are inside HSF/VSF range it's perfectly safe to
play with or you can ask for warranty...

   | So I think I can put HSF = 70000 and VSF = 160 but what about
   | DCF ? Is DCF = 100 proper? How can I get it ?

check modeplot utility - it shows you nicely what your options are.
BTW, why do you need DCF? There is no need to set DCF in XF86config,
just put HSF and VSF and start playing with modes

   | 
   | So shown below the  Maximum allowed dot-clock: 250.000 MHz
   | Is it connected to DCF ?

   Yup, but you have to choose the minimum of the card and the monitor.

   Conclusion:  maximum DCF = 100.

around 120 for 1280x1024x66Hz


OK