Service manual
Commercial
in
confidence
SMARTFIND
NAVTEX
service
manual
Page
27
5.3.
System
Block
Diagram
Provided
for
information
only.
Outline
circuit
description
The
unit
runs
off
a
10.8
to
31.2V
DC
power
input
protected
by
auto
resetting
fuse.
A
dc-dc
converter
provides
a
number
of
internal
voltage
rails
used
by
the
LCD,
processor
and
receivers.
The
processor
provides
for
control
of
the
other
sections
of
the
circuitry.
Flash
memory
provides
for
program
storage,
and
long
term
storage
of
NAVTEX
data
where
required.
SDRAM
provides
for
storage
of
volatile
data.
At
power
up
an
application
code
is
decompressed
from
FLASH
to
SDRAM
and
the
code
is
run
from
SDRAM.
A
buzzer
is
provided
to
confirm
key
presses
and
sound
alarms.
A
keyboard
matrix
and
two
switches
are
provided
for
the
user
controls
and
link
directly
to
the
processor.
Green
LEDs
provided
for
back
lighting
of
the
keyboard.
These
are
of
variable
brightness.
A
red
LED
is
provided
for
status
warnings.
Data
interfaces
for
communicating
with
external
equipment
are
provided
on
the
9
and
15
way
rear
connectors.
A
colour
STN
LCD
is
driven
directly
by
the
processor
this
has
a
high
voltage
CCFL
backlight
with
adjustable
brightness.
Active
and
passive
NAVTEX
antenna
types
are
supported
by
a
switchable
onboard
power
supply
and
current
monitoring.
Three
parallel
receivers,
one
to
each
receive
frequency
provide
simultaneous
operation
at
all
times
on
each
NAVTEX
frequency.
And
employ
direct
conversion
down
to
base-band
to
generate
the
I
&
Q
signal
to
the
demodulation
software.
A
RSSI
(Receiver
Signal
Strength
Indicator)
signal
is
derived
from
the
AGC
signal
as
a
diagnostics
aid.
Receiver
1
Receiver
2
Receiver
3
Signal
processo
r
&
CPU
Message
memory
IBS
port
Printer
port
INTEGRAL
DISPLAY
IEC61162
RS232