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Physio Control LIFEPAK 9
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LIFEPAK
9
shock
advisory
adapter
Service
Manual
1-8
Microcontroller
Core
The
Microcontroller
Core
circuit
analyzes
patient
information
from
the
Preamp.
The
microcontroller
is
a
16-bit
microprocessor
with
an
internal
analog-to-digital
(A/D)
converter
required
for
ECG
signal
analysis.
Microcontroller
U17
is
the
main
component
and
supporting
components
are
the
following:
EPROM
U14,
RAM
U15,
latch
U16,
clock
U13,
and
NAND
gate
U12.
Clock
oscillator
U13
generates
the
microcontroller
operating
10MHz
clock
pulse.
NAND
gate
U12B
and
U12C
buffer
the
output
of
U13
to
the
microcontroller.
A
reset
circuit
on
the
+5V
ISO
supply
protects
the
microcontroller
from
power-up
transients
and
defibrillation
pulses.
The
reset
circuit
generates
an
active-low
reset
signal
at
the
output
of
inverter
Ul
1A.
When
+5V
ISO
power
is
removed,
both
inputs
of
NAND
gate
U12A
switch
low,
producing
a
logic
high
on
the
output.
U11A
inverts
the
signal
to
reset
the
microprocessor.
The
reset
pulse
is
active
for
a
period
between
Sms
and
50ms
each
time
the
+5V
ISO
supply
is
turned
on.
An
RC
network
consisting
of
R27
and
C13
at
U12A
pin
2
delay
the
+5V
ISO
supply,
giving
the
microcontroller
sufficient
off-time
to
protect
itself.
U17
Microcontroller
protection
during
defibrillation
starts
when
the
Microcontroller
Inhibit
circuit
shuts
down
the
Power
Supply
circuit
and
holds
U17
in
reset.
With
the
Power
Supply
disabled,
the
negative
voltage
at
the
gate
of
Q8
decays
to
zero
volts
through
R35
and
C34.
Capacitor
C13,
normally
charged,
must
be
discharged
to
hold
the
microcontroller
in
reset.
When
the
voltage
at
the
gate
of
Q8
is
at
zero
volts,
Q8 conducts
and
discharges
C13.
When
either
of
the
input
pins
|
or
2
are
low,
the
microcontroller
resets.
External
memory
for
the
microcontroller
consists
of
EPROM
U14
and
RAM
U15.
The
EPROM
contains
the
program
that
controls
the
microcontroller
functions
and
holds
the
algorithm
used
to
analyze
the
ECG
signal.
The
RAM
is
used
as
temporary
storage
for
patient
information,
serial
communication
with
the
Instrument
Interface
circuit,
and
as
a
scratchpad
memory
for
computation.
All
Rights
Reserved
©
November
1994
Physio—Control
Corporation

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