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VGA mode 0x13 in pmode
Posted: Mon Sep 27, 2004 1:56 pm
by HOS
Hello,
without using the BIOS routines are their ports to write to or some other method to switch between 80x25 character mode and VGA graphics mode 0x13?
thanks
Re:VGA mode 0x13 in pmode
Posted: Mon Sep 27, 2004 3:37 pm
by Dreamsmith
You can always switch from any one video mode to any other without using the BIOS. However, what I/O ports and/or memory mapped I/O locations you need to access will vary from card to card. If you have a Virtual-8086 monitor, you can log which I/O ports and such are being accessed by the BIOS to enable a particular video mode. OTOH, if you have a Virtual-8086 monitor, you don't need to bother...
That having been said, the good old-fashioned VGA video modes can
usually be enabled in a fairly standard manner, due to backwards compatibility concerns with most video card makers. You might want to check here:
http://my.execpc.com/~geezer/osd/graphics/modes.c
Re:VGA mode 0x13 in pmode
Posted: Mon Sep 27, 2004 4:57 pm
by HOS
OK thank you, that looks like it will do what i want to do... i tried searching for a vga specification - does such a thing exist? something that says what each byte going to each port does? or is it better to mimic and not ask questions?
Re:VGA mode 0x13 in pmode
Posted: Mon Sep 27, 2004 6:27 pm
by Colonel Kernel
This is a pretty good reference:
http://osdev.neopages.net/FreeVGA/vga/vga.htm
Unfortunately, it doesn't have anything like a "how-to" on mode switching (I've been looking for the same thing recently). But with the above reference, it ought to be possible to figure out what the sample code is doing... hopefully...
Re:VGA mode 0x13 in pmode
Posted: Tue Sep 28, 2004 1:20 am
by bubach