Alpha Video
Alpha
video is
stored
in
on-board
RAM
and
provides 25 lines
of
text
with
80
characters
per
line. Provisions for inverse video
and
half-bright user-definable key labels
in
the
bottom
two
display lines
are
enabled
through
software programming.
Text
is 8-bit ASCII modified for
the
monitors
supported.
A switch determines
whether
Katakana
or
Roman
8
character
font will
be
used.
Configuration Switches
Two
switches
determine
display refresh
rate
and
alpha
character
font. Refresh
rate
is
determined
by
the
switch
farthest
from
the
edge connectors
and
should
be
set
to
the
line voltage frequency.
Otherwise,
the
monitor's
display may flicker. A 50 Hz
and
60 Hz position is available
and
the
printed
circuit
board
is labeled accordingly
next
to
this
switch.
The
switch
nearest
the
edge connectors determines
the
character
font.
When
the
computer
system
is used in
Japan,
or
when BASIC
or
Pascal
operating
systems
with
revisions lower
than
3.0 is used,
this
switch should
be
placed in
the
0 position
to
enable
the
Katakana
characters
to
be
displayed. For all
other
countries,
the
switch should
be
placed in
the
1 position
to
enable
the
Roman
8 style of characters. Labeling on
the
printed
circuit
board
next
to
the
switch
with
a 0
and
1 identifies
the
respective switch positions.
Video Output
Alpha
and/or
graphics Video is combined with sync pulses from
the
tilning circuits as a com-
posite video signal. Video
is
output
from
the
Monitor
BNC
connector on
the
video
card's
rear
panel.
When
graphics mode
is
selected by software, graphics video from
the
graphics
card
is
input·
to
the
video
card
and
output
from
the
BNC
connector labeled Monitor.
When
alpha
video is
selected,
alpha
video is
output
from
the
same connector.
This
type
of
video is called
separate
alpha/
graphics video.
For systems using a color
monitor
with
this
card
set,
the
green video with sync
is
input
from
the
color video circuits in
the
computer
and
is
processed
the
same as composite monochrOlne
video.
The
Monitor
output,
which in
this
case is green video
with
sync,
is
connected
to
the
green
input
connector on
the
color monitor. Red
and
Blue
outputs
from
the
video
board
in
the
system slot
are
fed directly
to
the
Red
and
Blue
input
connectors on
the
color monitor.
Graphics Card
Circuits
required
to
control
the
graphics video
are
on
the
graphics card.
This
card
is
the
same
one used
with
the
HP
98204 Composite Video
Cards
for Series 200 computers.
Graphics Video
Inputs
from
the
video
card
through
the
ribbon
cable
are
converted
to
a 390 by 512 graphics
display
and
stored
in
on-board
RAM. Graphics memory is organized such
that
the
first 8 pixels
displayed in
the
upper
left-hand
corner
of
the
display correspond
to
the
first
byte
of
memory
in graphics RAM. Each succeeding
byte
corresponds
to
the
next
8 pixels
to
the
right in
the
graphics display.
Graphics Video Output
Graphics
video
is
sent back
to
the
video
card
through
the
ribbon
cable connector.
116
Functional Description
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