Date: Tue, 13 May 1997 19:21:21 -0600 From: spector AT EnchantedLearning DOT com Subject: Re: Non-standard video modes (New video mode?) Newsgroups: comp.os.msdos.djgpp Message-ID: <863568824.24177@dejanews.com> Reply-To: spector AT EnchantedLearning DOT com Organization: Enchanted Learning Software References: <33741974 DOT 4D77 AT EnchantedLearning DOT com> Lines: 67 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Precedence: bulk Thanks for the information, Shawn. I read the documentation you suggested, as well as some others, and was able to put together a 512x384 256-color video mode similar to mode-X. There's a catch though -- to get it to work, I need to store a '11' in the two Clock Select (CS) bits in the VGA Miscellaneous Output Register. The meaning of this is completely omitted in all the documentation I've been able to locate (2 books plus assorted files on the net). These bits control the VGA clock frequency (00 = 25-MHz, 01 = 28-MHz, 10 = external clock, but 11 is not even mentioned as a possibility in the documentation). Does anyone know what this does? (My guess is that maybe it doubles the clock frequency to something like 50 MHz, but I don't know.) Is this a Super VGA extension? And is this something that will work across the gamut of SVGA video cards, or does it just happen to work on the one I have (S3 Virge)? Thanks in advance for any clues as to how this is working :-). (Or, better yet, does anybody know how to make a 512x384 8-bit mode with standard VGA? I've tried, but I haven't yet been able to get my monitor to stop rolling and sync correctly -- maybe VGA just doesn't support a high enough dot frequency to do this.) Mitchell -- Mitchell Spector Enchanted Learning Software E-mail: spector AT EnchantedLearning DOT com Web site: http://www.EnchantedLearning.com In article , Shawn Hargreaves wrote: > > Mitchell Spector writes: > >How does one go about programming support for non-standard video modes? > >(I'd like 512x384 with 8-bit color, implemented so that it's useable by > >Allegro.) UniVBE is able to do this even when using video cards that > >ostensibly don't support that resolution, and I'm curious how this can > >be done. > > UniVBE does it by having lots of very chipset-specific code for each > card that it supports: not a realistic option for most people! > > It is possible to get quite a lot of non-standard VGA modes by entering > mode-X and tweaking the VGA register settings, but I've never heard of > 512x384 being accessible in this way (certainly modes like 360x480, > 376x282, and 400x600 are quite possible, even if they don't work on > every monitor). To see how these are done, look at the modex.c file from > Allegro. It enters standard mode 13h and then tweaks the appropriate > registers, using some tables that list the changes required for each > video mode. > > >Thanks in advance for any pointers to documentation or other > >information. > > Get VGADOC3 from x2ftp.oulu.fi (I can't remember the exact path, it's in > something like /pub/msdos/programming/docs). > > -- > Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/ > Beauty is a French phonetic corruption of a short cloth neck ornament. -------------------==== Posted via Deja News ====----------------------- http://www.dejanews.com/ Search, Read, Post to Usenet