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Sigma 6000+ - Page 24

Sigma 6000+
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THEORY
OF
OPERATION
(Continued)
Functions
of
the
LSI
Chip
(019)
Interrupt
Controller
(Continued)
8.
DROP
SENSOR
pin
11
—
pulses
signal
the
microprocessor
that
a
drop
was
not
detected
by
the
flow
sensor
(when
installed).
Other
Functions
1.
CLOCK
pin
22
—
clock
input
for
time
control
2.
Pins
61
and
62
—
latched
outputs
control
motor
drive
current;
43
—
sensor
enable;
pin
67
—
audio
alarm
activation
and
audio
frequency:.pin
64
—
display
blanking;
and
риз
44
—
3
hour
memory.’
Motor
Drive
Circuit
(Chopper
Drive)
A
pulse
train
is
emitted
from
LSI
U19
pin
65
that
is
proportional
to
the
speed
at
which
the
motor
is
to
turn
|
and
connects
to
U1
pins
3
and
11
and
U14
pin
1.
Ul
is
a
4013,
dual
clocked
R/S
latch.
The
signal
going
into
pins
3
and
11
produces
a
two-phase
signal
from
pins
1
and
12.
This
two
phase
signal
is
conditioned
with
“INVERTERS”
from
U2,
“AND”.
gates
from
U3,
“OR”
gates
from
U4
and
U6
and
two
more
“D”
latches
from U5
to
combine
the
original
inverted
clock
signal
from
U14
pin
2
with
the
two
phase
signals
to
allow
%
step
operation
of
a
two
phase
stepper.
The
signals
from
U19
pins
61
and
62
are
motor
current control
signals
and
are
used
with
“OR”
gates
from
U6
to
send
the
required
signals
to
the
motor
driver
IC’s
U7
and
U12
to
allow
the
necessary
current
levels
to
be
delivered
to
the
motor
windings.
U7
and
U12
are
similar
to
switching
voltage
regulators
in
that
they
switch
the
voltage
on
and
off
rapidly
to
control
the
current
drawn
by
the
load.
This
switching
allows
more
of
the
current
to
do
useful
work
in
the
motor
by
circulating
through
the
windings
during
the
off
cycles.
The
level
of
current
at
which
the
switching
begins
is
controlled
by
pins
9
and
7
of
U7
and
U12,
and
the
voltage
developed
across
R4
and
R13
due
to
current
drawn
by
the
motor.
The
rate
at
which
the
chopping
occurs
is
controlled
by
R2
and
C2
for
U7,
and
Ril
and
C18
for
U12.
Ultrasonic
Sensor
Drive
The
frequency
is
derived
from
the
2.4576Mhz
crystal
frequency
which
is
fed
into
U19
pin
22.
Here
it
is
_
divided
to
obtain
approximately
250Khz
which
is
then
used
to
drive
the
front
panel
sensor.
This
frequency
output,
U19
pin
43,
connects
to
the
sensor
drive
circuit.
L1
is
an
inductor
used
to
provide
phase
correction
for
the
signal.
Сб,
D5,
RS,
Qi,
Li,
R10
and
SWI
select
the
frequency
output
and
condition
it.
Axe
Circuit
This
circuit
is
designed
to
prevent
the
improper
operation
of
the
pumping
mechanism
in
the
6000+
that
could
result
from
a
loop
outside
of
the
program
or
a
failure
and
a
subsequent
lock
up
of
the
microprocessor.
ln
the
main
section
of
the
unit's
software
(program),
a
command
is
inserted
which
causes
every
loop
within
the
main
program
to
output
a
signal
pulse
on
pin
7
of
U25
and
the
CPU.
This
pulse
train
is
directed
through
R49
and
C39
to
the
gate
of
FET
Q10
which
pulses
it
on,
Section
1
Page
16

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