List
of
Contents
Page
INTRODUCTION ............ ................ ....... .......... ............. 1
DESCRIPTION ..............................................
~
................ 2
General ............................................................................ 2
Mode Selection ............................................................... 8
CRTC DETAIL ............................................................ 10
General ......................................................................... 10
Register Description .................................................... 13
Initialising the CR TC
.. ..
..
.... .........
..
.... .... .
..
........ ......... . 16
CRTC Connections ..................................................... 1 7
SCREEN
RAM
............................................................. 19
General ......................................................................... 19
Text Mode ....................................................................
20
Graphics Mode ............................................................. 22
SYSTEM RAM UTILISATION ................................... 23
General ......................................................................... 23
Text Mode ....................................................................
24
Graphics Mode ............................................................. 25
DISPLAYUNITCONNECTORDETAIL .................. 26
List
of
Illustrations
Figure
CRT
control
circuitry
block
diagram
............................ 1
CR
TC
block
diagram
................................................. ..... 2
Text
Screen
..................................................................... 3
Graphics
Screen
.............................................................. 4
INTRODUCTION
The
CRT
Control
circuitry
is
located
on
the
System
Board
and
provides
the
interface
for
displaying
text
or
graphics
on
the
screen
of a
high
resolution
monochrome
display
unit.
In
the
text
mode
of
operation
(alphanumerics), a
display
area
of
80
characters
by
25
lines
is
available,
using
a
character
cell
of 10
pixels
wide
by
16 pixels
high.
The
characters
for
display
are
accessed
from
a
character
font
loaded
by
the
BIOS
into
the
System
RAM.
Each
character
can
be
modified
using
a
series
of
programmable
display
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