need info about BIOS int 10h video pagesFrom: bilsch01Newsgroups:
A noiseless patient Spider
Fri, 13 Dec 2019 08:24 UTC
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Re: need info about BIOS int 10h video pagesFrom: JJNewsgroups:
Fri, 13 Dec 2019 15:50 UTC
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On Fri, 13 Dec 2019 00:24:55 -0800, bilsch01 wrote:
Ralf Brown RBIL int 10h mentions pages:
ah=5 select active display page
ah=0xe bh=page number
RBIL Table 00010 has a column heading for display pages.
I searched around and can't find definition or details about the pages.
What are they? How does one page differ from another? In particular are
there address ranges associated with the pages?
TIA. Bill S.
Video page is basically a division of the video memory of the current video
For example, in 80x25 color text mode 03h, the used video memory is at
B800:0000 to B800:7FFFF or at linear address 0xB8000 to 0xBFFFF, fot a total
Each video page size for that video mode is 4096 bytes. Video page index 0
is at 0xB8000-0xB8FFF, index 1 is at 0xB9000-0xB9FFF, and so on and up to
the last index 7 at 0xBF000-0xBFFFF.
The 80x25 screen only uses 80x25x2 bytes or 4000 bytes or 0xFA0 bytes. So,
there's actually 96 bytes of unused memory at the end of each video page.
Video page for other video mode has the same concept, but with different
size of video page because the memory needed for a specific video mode
differs. e.g. 40x25 text would have 16 video pages. 320x200 16 color graphic
video mode would have 2 video pages, because it needs 32000 bytes. i.e. at
A0000-A7FFF and A8000-AFFFF. 640x200 16 color video mode would only have 1
video page because it needs 64000 bytes of memory. The remaining 1536 bytes
of A0000-AFFFF memory is not enough for another video page.