Reply 20 of 55, by darry
underage wrote on 2021-06-19, 20:38:... […]
dvwjr wrote on 2008-07-03, 09:11:for NVidia video adapters one must dis-assemble the vBIOS code to determine the location of the various tables which determine the VGA and VESA modes and 'dot-clock' values to change refresh rates.
dvwjr wrote on 2008-07-03, 09:11:Once you program the CRTC registers directly, you can do almost anything in DOS... However, if you are going to use the standard VGA or VESA modes defined in the vBIOS via the Int 10h interface, the VESA video mode refresh rate might as well be changed with the standard VESA 3.0 vBIOS API, which is supported via the Int 10h/AX=4F02h ES:DI->CRTC information block with bit 11 of the BX=requested video mode bit set.
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Another option to consider to get 70Hz out of at least some Nvidia cards in DOS and using DVI, however, is described in these threads :
[HOWTO] Running DOS games natively with perfect 4:3 aspect ratio @ 70 Hz over DVI (using a DIY EDID emulator)
70Hz in pure DOS at 1600x1200 (or other) over DVI on an old card (FX5900) with modern monitor is possible (using a commercially available EDID emulator)
This approach has been tested successfully on multiple Nvidia cards, including a Geforce 6800 GT .
EDIT : Just saw that you intend to use a CRT, so this will not be applicable to your use case .