Video
RAM
Both
high-
and
medium-resolution color video
boards
have four 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 also uses four planes
but
requires
16
memory chips
per
plane.
Resolution
is
1024 X 768 single pixels. Video memory uses nybble (4-bit) wide Display RAM
(DRAM).
Table 3-3 shows how
the
display RAM is organized for
the
desired resolution for each board.
Table 3-3. Video
Board
RAM
and
Resolution
Video Board
HP
98542 Med-Res
Monochrome
HP
98543 Med-Res Color
HP
98544 High-Res
Monochrome
HP
98545 High-Res Color
Color
Mapping
Number
of
16K
X 4
RAM
Chips
8
32
16
64
Total
RAM
per
Board
64K
bytes
256K
bytes
128K
bytes
512K
bytes
Resolution
on
Monitor
512
by
400
512
by
400
1024
by
768
1024
by
768
Each color
board
has four 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 Contollers
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
T)~'3play
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.
62
Functional Description
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