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> DOS > how to tune screen refresh rate under dos vbe 2.0? |
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neonz 06 Nov 2004, 18:07
VBE 2.0 does not have standartized API for changing refresh rate. VBE 3.0 have API for changing refresh but it is supported only by very new adapters (3dfx, nVidia, etc...).
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06 Nov 2004, 18:07 |
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cylo 06 Nov 2004, 18:27
so the only way is to program the chip directly? what registers i have to look for?
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06 Nov 2004, 18:27 |
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MCD 29 Nov 2004, 18:02
Lookily, many standard VGA-registers are accessible in VESA-modes too.
You tweak a bit around and test what changing of standard VGA-registers makes what changings in your VESA mode. I used this way to emulate a vesa 512*384 mode starting from a 640*480/400 mode by simply writing something to miscellaneous output register, but this requires somewhat experimenting with graphics card, and when writing wrong things, the screen will often become blank. (Ctrl+C/Break or Ctrl+Alt+Delete ) Another thing I did was changing the refresh rate of the standard vga 80*25/50 text mode by just setting a vesamode BEFORE setting to a textmode => this changes external pixel clock, which must be enabled in some VGA CRTC-register. But all of these tweaking should be accomplished with lots of testing on many different machines, since I'm not sure how they work on other PCs, e.g. they are not (well) documented. (I think so) _________________ MCD - the inevitable return of the Mad Computer Doggy -||__/ .|+-~ .|| || Last edited by MCD on 29 Nov 2004, 18:04; edited 1 time in total |
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29 Nov 2004, 18:02 |
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MCD 29 Nov 2004, 18:03
I assume that you have a copy of Ralf Brown's Interrupt list. A "must-read"
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29 Nov 2004, 18:03 |
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