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How many MB of VRam are emulated in DosBox?

I'm writing 16bit software in NASM that includes the needed opcodes to switch to VESA video modes, including 640x480 256 color mode. I am discovering that DosBox doesn't do well with that mode. It doesn't let me use any more VRAM than needed for 640x400 256 color mode (80-pixels shorter in the …

Re: Question about DOS 16 color modes.

Thanks. I'll have to check that out. I also discovered something. If I set the chaining bit in graphics card sequencer register 4. It does something quite interesting (at least in DosBox, not sure about real hardware). It changes it from the normal EGA image-planar mode (where you have to select …

Re: Question about DOS 16 color modes.

The original IBM EGA manual describes it's registers, maybe it could be useful http://minuszerodegrees.net/oa/OA%20-%20IBM%20Enhanced%20Graphics%20Adapter.pdf Also I can try those experiments with real hardware (nearly any kind of known video card), I'm very interested to test if it's possible to …

Re: Question about DOS 16 color modes.

The idea you describe (enabling chain-4 mode on 16-color modes) doesn't work on EGA cards, because that mode hasn't been implemented until VGA. But it should work perfectly on any VGA compatible card. The drawback of that approach is that you limit the video memory available from 256KB to 64KB, so …

Re: Question about DOS 16 color modes.

Using EGA/VGA Write Mode 2 it's a little bit complicated, you should read this book, it explains it very well with some examples http://vtda.org/books/Computing/Programming/EGA-VGA-ProgrammersReferenceGuide2ndEd_BradleyDyckKliewer.pdf The VGA 80x200 mode is set by changing the number of scanlines …

Re: Question about DOS 16 color modes.

With EGA cards you can write pixels to VRAM in a chunky way using Write Mode 2, BUT it's much slower than writing plane by plane (it requires a read and a write operation from the video card for each pixel). I guess the only way to do bit-packed 16 color graphics is using the text modes (VGA …

Question about DOS 16 color modes.

I know in 16-color modes, such as EGA (320x200 and 640x200) and VGA (640x350), you have normally have to put the bits in one bitplane at a time (using a control register on the graphics card via the OUT x86 instruction, to set the plane that you are about to copy the image data to). However I also, …

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