Theory
of
Operation
2-37
Controller
The
controller regulates the entire interface between the lOP bus
and
the display.
The
controller
operates
in
two basic nl0des: display
mode
and
lOP mode.
In
display mode, the controller transfers
data from the frame buffer to the line buffer. Display
mode
occupies the controller approximately
12%
of the time. For
about
88%
of the time the controller
is
in
lOP mode, responding to the lOP,
requesting frame buffer updates,
and
controlling the updates.
98760A Standard Color Graphics Display
The
98760A
display receives data from the CPU, buffers
it
in
RAM,
and
displays
it
on
the CRT
screen.
The display
is
a memory mapped, raster scan CRT. A total of
256
characters
can
be
displayed,
including
all
128
ASCII characters. The display uses either the English
or
Japanese
Katakana
character set, depending
on
which ROM
is
selected
and
inserted at the factory. Character display
matrix
is
720
dots (horizontal) by
390
dots (vertical).
The bottom of the screen can
be
set
up
to display
in
half-bright, inverse video,
on
a line-by-line
basis. This feature visually separates softkey labels from the remainder of the screen.
The
CRT display consists of these assemblies:
• Alpha/Interface Board
• Graphics/Digital Video Board
• Video Board
•
Sweep
Board
• CRT N
oke
Assembly
• Display Power Supply
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