In
APA
mode, there are two resolutions available; 320x200 and
640x200. In the 320x200, each (picture element) pel may have one
of
four colors. The background color (color 0) may be any
of
the
16
possible colors. The remaining 3 colors come from one
of
the two
software selectable palettes. One palette contains red/green/brown,
the other contains cyan/magenta/white.
~
The 640x200 mode is only available in black and white since
the
full
16KB of storage
is
used to define the on or off state
of
the pel.
The adapter operates in noninterlace mode at either
7 or 14 megahertz
(Mhz) video bandwidth depending on the mode
of
operation selected.
In
NN
mode, characters are formed from a
ROM
character generator.
The character generator contains dot patterns for 256 characters.
The character set contains the following major grouping
of
characters.
Sixteen special characters for game support,
15
characters for support
of
word processing editing functions, the standard 96
ASCII
graphic
set, 48 characters to support foreign languages, 48 characters for
business block graphics allowing drawing
of
charts, boxes and tables
using single and double lines, 16 of the most often used Greek
characters, and
15
of
the most often used scientific notation characters.
The Color/Graphics Monitor Adapter function is packaged on a single
card which fits into one
of
the
five
System Expansions Slots on the
r"'\
System Board. The direct drive and composite video ports are right-
angle mounted connectors
at
the rear
of
the adapter and extend through
the rear panel
of
the System Unit.
The display adapter is implemented using a Motorola 6845
CRT
controller device. This adapter is highly programmable with respect to
raster and character parameters. Thus, many additional modes are
possible with clever programming
of
the adapter. A block diagram
of
the Color/Graphics Adapter
is
on the following page.
2-46
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