Video RAM
Both
high-
and
medium-resolution color video
boards
have four
or
six planes
of
memory.
The
medium-resolution
board
uses eight memory chips
per
plane.
This
is enough
to
display 512
doubled pixels by
400
scan
lines. High-resolution
boards
requires more memory chips
per
plane.
Resolution is
1024 by 768 single pixels.
Table 3-6 shows how
the
display
RAM
is
organized for
the
desired resolution for each
board.
Table 3-6. Video Board RAM and Resolution
Video Board
RAM chips Total RAM
Resolution
HP
98542 Med-Res Monochrome
8
64
Kbytes
512
by 400
HP
98543 Med-Res Color
32
256
Kbytes
512
by 400
HP
98544 High-Res Monochrome
16
128
Kbytes 1024 by
768
HP
98547 High-Res Color
64
512
Kbytes
1024 by
768
Color Mapping
Color
boards
have four
or
six
plane
color mapping.
Mapping
is
entirely
under
control
of
the
Frame
Buffer Controller.
The
high-resolution
board
has more
RAM
than
the
medium-resolution
board.
Display Controller
The
Display Controllers
are
the
heart
of
these video boards.
They
provide complete video
control
and
bit-mapped
alpha
support
for one graphics plane. Interfacing directly with
the
computer
CPU,
it
integrates
and
manages
most
display functions.
The
functions
of
the
Display
Controllers are:
•
Provide
horizontal
and
vertical timing signals
to
the
sweep section
of
the
video
board.
•
Provide
refresh
data
to
the
frame buffer.
•
Generate
the
blinking underline cursor.
•
Enable
window move operations.
•
Output
video
and
sync signals
to
the
frame buffers.
Architecture
provides for
either
color
or
grey-scale monochromatic display use.
The
display
is
organized
with
one memory
byte
for each display pixel.
This
corresponds
to
a
maximum
capability
of
eight planes
with
one
byte
per
pixel
per
plane. Each
bit
in
the
byte
goes
to
a
separate
frame buffer memory plane. Pixel
data
is
transferred
32
bits
(or pixels)
at
a
time
by
read
and
write
operations
with
display
RAM
by
the
video
board.
Logic internal
to
this
chip
enables software
to
perform byte-per-pixel access.
96
Functional Description
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