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INT 10h, 12h (18) Alternate Select EGA
Returns information on the Enhanced Display Adapter (EGA) and allows
the selection of an alternative EGA Print Screen routine.
---------------------------------------------------------------------------
BL = 10h Return EGA Information
On entry: BL 10h
AH 12h
Returns: BH Display mode in effect
00h Color mode (3Dxh address)
01h Monochrome mode (3Bxh address)
BL EGA Memory
00h 64K
01h 128K
02h 192K
03h 256K
CH Adapter bits
CL Switch setting
BL = 20h Select Alternative EGA Print Screen Routine
On entry: BL 20h
AH 12h
BL = 30h Select Scan Lines (VGA text)
On entry: BL 30h
AH 12h
AL 0 . 200 scan lines
1 . 350 scan lines
2 . 400 scan lines
Returns: AL 12h . Function supported
BL = 31h Enable/disable Default Palette Loading (MCGA, VGA)
On entry: BL 31h
AH 12h
AL 0 . Enable default palette loading
1 . Disable default palette loading
Returns: AL 12h . Function supported
BL = 32h Enable/disable CPU Access to Video RAM (MCGA, VGA)
On entry: BL 32h
AH 12h
AL 0 . Enable access
1 . Disable access
Returns: AL 12h . Function supported
BL = 33h Enable/disable grey scale summing (MCGA, VGA)
On entry: BL 33h
AH 12h
AL 0 . Enable summing
1 . Disable summing
Returns: AL 12h . Function supported
BL = 34h Enable/disable ROM BIOS cursor emulation (VGA)
On entry: BL 34h
AH 12h
AL 0 . Enable cursor emulation
1 . Disable cursor emulation
Returns: AL 12h . Function supported
BL = 35h Display Switch (MCGA, VGA)
On entry: BL 35h
AH 12h
AL 0 . Initial adapter off
ES:DX = address of switch
state save area (128 bytes)
1 . Initial system board video on
2 . Switch off active video
ES:DX = address of switch
state save area (128 bytes)
3 . Switch on inactive video
ES:DX = address of switch
state save area (128 bytes)
Returns: AL 12h . Function supported
BL = 36h Video Screen On/off (VGA)
On entry: BL 36h
AH 12h
AL 0 . Screen on
1 . Screen off
Returns: AL 12h . Function supported
---------------------------------------------------------------------------
Notes: The value returned in CL (Switch setting) represents
the DIP switch settings on the EGA. The Adapter bits
(CH) is defined as follows:
Adapter bits (CH)
7 6 5 4 3 2 1 0
x x x x . . . . Unused
. . . . x x . . Reserved
. . , . . . x . FEAT1 (pin 17)
. . . . . . . x FEAT0 (pin 19)
To print the screen contents when the number of rows
changes, use Subservice 20h (Set Alternative Print
Screen) to install a Print Screen routine that will
work correctly with the row change.
Subservice 30h lets you set the number of VGA text mode scan lines. The
vertical resolution does not change until the next time a program uses
INT 10h, Subservice 00h to change the video mode.
Subservice 31h lets you enable or disable palette loading when the ROM
BIOS sets up an MCGA or VGA mode.
Subservice 32h lets you disable a CPU's access to video RAM. If you have
two video systems and the memory address of one overlaps the other, you
can disable one with this Subservice.
Subservice 33h lets you convert MCGA or VGA colors to a grey scale.
Under this Subservice, BIOS will average colors to grey when you next set
the video mode.
Subservice 34h enables or disables text-mode cursor emulation on the VGA.
If you set emulation, BIOS emulates CGA text-mode cursor sizing whenever
you change the video mode.
Subservice 35h lets you switch between displays -- usually between a MCGA
and a VGA. (You need to disable overlapping memory with subservice 32h
first.)
Subservice 36h lets you enable or disable VGA video refresh. When you
disable refresh, the screen is blank, but you can read from and write to
the video buffer in memory faster. If you want your program to swap
screens as fast as possible, you might consider turning off video refresh
while doing it.
See Also:
INT 10h, 11h
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