Display
Board
4-14
Each
display
driver
(U6,
UI0,
and
U14)
can
drive
up
to
eight
banks
of
eight LEDs
by
multiplexing
the
time
that
each
bank
is
turned
on. The
banks
can
be
wired
together
to
increase
the
time
that
a
group
of
LEDs is
on,
effectively increasing
the
brightness
of
that
group.
UI0
drives
the
discrete LEDs
and
the
CEM
LED. These
include
green
indicators for
the
bipolar
modes
(Precise,
Standard,
and
Macro),
the
cut
modes
(Low,
Pure,
and
Blend),
and
the
coag
modes
(Desiccate, Fulgurate,
and
Spray).
The
anode
of
the
mode
selection LEDs are tied to
driver
UlO.
By
using
pairs
of
the
driver
digit
lines,
the
duty
ratio for these LEDs is
effectively
1/4.
U6
drives
the
seven-segment
displays
that
indicate
power
settings. U4
and
US indicate
the
bipolar
power
setting, U7-U9 indicate
the
cut
power
setting,
and
UU-U13
indicate
the
coag
power
setting. The
anodes
of
these
displays
are
each
tied to
only
one
digit
line
of
the
driver. The effective
duty
cycle
is
1/8
for
each seven-segment display.
Some filtering
components
are
associated
with
U6,
UI0,
and
U14. Bypass
capacitors C3, C4, C7, C8, C9,
and
ClO
are
connected
between
+
SV
and
DGND. C3, C4,
and
ClO
have
a relatively
small
capacitance
value
of
0.1
pF
to filter
higher
frequency noise. C7,
CS,
and
C9
have
a relatively
large capacitance
value
of
47
pF
to
supply
the large spikes
of
current
for
the
LEDs
generated
by
the
multiplexing action
of
the
drivers,
which
typically occurs
at
250 Hz.
Resistor
array
RIB reduces
the
input
impedance
of
the
display
driver
inputs
as
seen
by
the
main
microcontroller
on
the
Control
board.
This
rounds
off
the
edges
of
these digital signals,
reducing
high
frequency
emissions. The
lowered
impedance
also reduces
the
susceptibility
of
the
circuit to noise
from
other
circuits.
CEM
Switch
Circuit
When
you
plug
a CUSA
handpiece
with
a CEM nosecone into
the
Monopolar
l/CEM
Instrument
receptacle,
the
small nonconductive
pin
in
the
plug
pushes
a
spring-loaded
plastic lever
arm
mounted
inside
the
front panel. This
lever
arm
activates a small switch
that
plugs
into
the
Display
board.
The
switch signal tells
the
microcontroller to limit the
power.
Mode
Selection
and
Power
Control
Switches
The
mode
selection
and
power
control switches
are
arranged
in
a matrix.
The
main
microcontroller selects a
bank
of
switches to
read
by
asserting a
bank
select
signal
(BANKO,
BANKl,
or
BANK2)
through
port
A
of
programmable
peripheral
U3
on
the
Control
board. These signals
are
buffered
by
Ql,
Q2,
and
Q3 respectively
and
become
the
switch
drive
signals
COMO,
COMl,
and
COM2.
Force
FXTM-C
Service
Manual
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