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Physio Control LIFEPAK 9 - Page 41

Physio Control LIFEPAK 9
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Description
1
the
timing
of
the
Video
RAM
(U21)
and
Font
EPROM
(U22)
addressing
during
CRT
scan
periods,
and
control
the
Video
RAM
addressing
during
CRT
retrace
periods.
The
Display
Gate
Array
uses
an
18-bit
counter
to
control
the
timing
of
the
vertical
and
horizontal
retrace
on
the
CRT.
The
lower
8
bits
correspond
to
256
rows,
and
the
upper
10
bits
correspond
to
768
columns
(scan
lines).
When
a
count
of
256
occurs,
U29
initiates
a
vertical retrace.
When
a
count
of
196,608
(256
x
768)
occurs,
the
gate
array
initiates
the
horizontal
retrace.
Four
separate
memory
loops
for
two
separate
trace
generators
in
the
Display
Gate
Array
format
the
ECG
signal
in
memory.
Formatting
occurs
during
horizontal
retrace.
An
internal
11-bit
counter
addresses
each
memory
loop.
Each
trace
generator
uses
one
memory
loop
for
the
high
point
of
the
scan
and
another
memory
loop
for
the
low
point
of the
scan.
The
trace
appearing
on
the
CRT
screen
is
created
by
turning
the
video
on
at
the
screen
location
that
corresponds
to
the
low
point,
and
turning
the
video
off
at
the
screen
location
that
corresponds
to
the
high
point.
This
saves
memory
space
in
Video
RAM
U21
since
the
only
data
loaded
in
memory
is
the
high
point
and
the
low
point
addresses
for
each
scan.
Serial
communication
between
the
Display
Gate
Array
and
the
Display/
Recorder
microprocessor
is
accomplished
by
the
following
control
lines:
H.RETR,
GO,
INCMEM,
and
TR/CHAR.
These
lines
enable
the
Display
Gate
Array
and
the
Display/Recorder
microprocessor
to
coordinate
the
storage
and
retrieval
of
ECG
and
character
data
in
the
Video
RAM
during
horizontal
retrace.
Figure
1-7
shows
the
control
line
timing
sequence.
H.
RETR
(IRQ1)
トド
ce
UPDATE
|
=
TR/CHAR
ο
|
Figure
1-7
Control
Line
Timing
MESSAGE
©
UPDATE
Data
from
the
Display/Recorder
microprocessor
loads
into
the
Video
RAM
memory
during
horizontal
retrace.
Six
ECG
samples
update
during
horizontal
retrace
to
smooth
scrolling
of
the
trace
displayed
on
the
CRT.
©
August
1993
Physio-Control
All
Rights
Reserved
1-27

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