Video Boards
Introduction
Video
boards
allow
the
computer
to
send
bit-mapped
display information
to
medium
or
high
resolution monitors.
The
user may
upgrade
his
computer
system
from
medium
to
high resolution
by installing a different
board.
Upgrading is accomplished
through
an
exchange program.
It
may
be
performed by
the
user
with
common
tools
without
CE
support.
One
monochromatic
and
two color video
boards
are
available for
the
HP
Series 300
computer
systems.
The
color
boards
provide four-plane color display capability allowing
the
user
to
display
16 colors from a
palette
of
over 16 million colors. A description
of
these
boards
follows:
•
HP
98542A Medium-Resolution Monochromatic Video Board.
This
version displays 512
by
400 pixels
and
drives
the
low resolution monochromatic monitors.
•
HP
9854:3A Medium-Resolution Color Video Board.
This
version displays 512 by 400
pixel pairs
and
drives
the
low-resolution color monitors.
•
HP
98544B High-Resolution Monochromatic Video Board.
This
version displays 1024 by
768 individual pixels
and
drives
the
high-resolution color monitors.
•
HP
98547A High-Resolution Color Video
Output
Board.
This
version displays 1024 by
768 individual pixels
and
drives
the
high-resolution color monitors.
These
boards
make extensive use of large scale
integrated
(LSI) circuits.
Up
to
six (depending
on
the
board)
NMOS III Display Controller chips provide
an
integrated
bit
mapped
display
with
window-nlove
hardware
and
frame buffer
support.
Color
mapping
is entirely
handled
by
another
NMOS III chip called
the
Frame
Buffer Controller.
This
chip performs color
mapping
and
D
to
A conversion. Video memory consists
of
uses nibble-wide (4-bit) Display
RAM
(DRAM).
The
major
difference between these assemblies is
the
amount
of
DRAM
each has.
Video
boards
perforrn
the
similar functions, which are:
•
Establish
display clock frequency in
the
computer
system.
• Initialize according
to
the
specific
monitor
used.
• Identifies itself
and
set
character
shape
by ID
/FONT
ROM.
•
Respond
to
interrupts
on
DIO/DIO-II
bus
to
change color
map
data.
• Control
the
display
RAM
maps.
• Color
boards
output
Red-Green/Sync-Blue
Video
to
the
color monitor.
• Monochromatic
boards
output
Video/Sync
to
the
monochromatic monitor.
Each
of
these
is
explained in
the
following functional description. Refer
to
Figure 3-21.
Functional Description
93
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