Juniper Systems Allegro DOS Manual - Manual (Page 124)

124 Allegro DOS Owner’s Manual
Keyboard and Video
A programmer can use the keyboard and video interrupt functions
to control the keyboard and video screens. These functions are
described below.
Keyboard Intercept Functions
BIOS interrupt 15h function 4Fh can be hooked to intercept raw (not
yet translated) scan codes from the keyboard, which are contained in
the AL register. The scan codes at this level are unique to the Allegro.
Refer to the system scan codes in the Scan Code Tables found at the
end of this chapter.
BIOS interrupt 15h function 4Eh can be hooked to intercept
translated scan codes from the keyboard, which are contained in the
AX register. The scan codes at this level are standard 2 byte scan/
ASCII character codes. The keys on the keyboard can be remapped to
output alternate characters through this interrupt.
Video
The Allegro display is a CGA compatible 320 x 200 pixel
monochrome LCD. Text mode (BIOS video mode 3) supports four
fonts which displays 40 columns x 25 lines, 40 x 16, 32 x 16, or 20 x 12
for the small, medium, large, or extra large fonts respectively. Font
may be toggled with a hot key or set programmatically through the
BIOS int 10h function 2E14h. A virtual 80 x 25 display with panning
capability is supported for all fonts. Text attributes can be set to
black/white, where CGA colors are mapped to either full on or full
off, and gray shades, where CGA colors map to various shades of
gray. This setting can be changed either in the System Setup program
or through BIOS int 10h function 2F23h.
Graphics modes supported are CGA mode 4 (320x200 pixel) with
four shades of gray, and CGA mode 6 (640x200 pixel) where pixels
are either on or off. Standard BIOS interrupt 10h functions are used
to set the video mode. Only modes 3, 4, and 6 are supported.
An autopan function can be enabled or disabled to cause the display
to pan with the cursor around the 80 x 25 virtual window. Extended
BIOS functions can be used to locate the display anywhere on the
virtual window. In this way multiple “pages” can be set up on the
single 80 x 25 window.
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