Eberline ESP-1 - Page 46

4-4
One-half
of
А104
is
interconnected
as
a
monostable
multivibrator
(TRIGGER).
The
Output
pulse
(TRIGGER)
width
is
set
by
R136-C112
time
constant.
The
other
half
of
A104
is
configured
as
an
oscillator.
It
is
running
while
the
trigger
output
(pin
11)
is
low,
driving
the
speaker
via
Q11
and
Q12.
The
input
signal
to
the
trigger
is
differentiated
by
C111-R135
to
prevent
excessive
trigger
pulse
widths.
А
The
alarm
is
activated
by
"ALM"
and
"SPKR"
set
low
(0
volts)
by
the
microcomputer.
This
sets
the
trigger
output
low
(pin
11),
turning
on
the
oscillator
frequency
to
the
speaker.
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"ALM"
low
also
activates
the
auxiliary
alarm
("A")
providing
an
active
low
output
for
extemal
indication (250 mA, 20 Vdc maximum).
Keyboard
The
switch
poles
are
etched
on
the
PC
board.
Contact
between
the
poles
is
made
by
a
conductive
pad
cast
into
each
keypad.
Pressing
a
keypad
effectively
short-circuits
the
poles.
The
ON/OFF
keypad
pulls
the
"RST"
(pin
9)
of
the
microcomputer
high.
This
causes
the
computer
to
reset
itself
and
begin
running
its
program
at
the
program
beginning
(see
figure
7-8).
The
LIGHT
keypad
causes
DS1
to
tum
on
via
Οἱ,
lighting
the
display.
All
other
keypads
are
inputs
to
the
microcomputer
via
its
input/output
(I/O)
port
P1,
which
is
configured
as
an
input
port
under
program
control.
These
inputs
are
normally
high.
Pressing
a
keypad
pulls
the
corresponding
port
input
low.
The
program
running
in
the
microcomputer
performs
the
contact
debounce,
determines
the
switch(es)
pressed,
and
logically
performs
the
task(s)
associated
with
the
keyboard
condition.
Microcomputer
Simply
stated,
a
computer
must
have
provisions
for
moving
data
in
and
out
(I/O),
a
logical
means
of
handling
and
saving
data
(memory),
and
logical
elements
to
control
I/O
and
memory
(central
processing
unit,
CPU).
To
perform
any
task,
the
CPU
must
execute
a
series
of
logical
steps
(program),
which
is
contained
in
read-only
memory
(ROM).
Memory
used
to
save
data
written
to
or
read
from
it
is
random-access
memory
(RAM).
The
RAM
contains
the
parameters(variables),
logic
flags,
data,
scratch
pads,
etc.,
used
by
the
program.
a. Inputs:
(1)
Keyboard
inputs
are
the
operator's
input
to
the
computer.
Under
program
control,
the
inputs
cause
the
task
associated
with
the
keypad(s)
to
be
performed
(see
section
III).
(2)
Mask
(S11)
switch
inputs
are
used
to
signal
(flag)
the
program
to
perform
certain
tasks
differently
or
omit
them
completely
(sce
section
Ш).
(3)
FHV
is
a
frequency,
the
rate
of
which
is
proportional
to
the
high
voltage
applied
to
the
detector
(probe).
When
the
program
is
displaying
high
voltage
(HV)
to
the
user,
it
converts
this
frequency
input
to
its
HV
equivalent.
(4)
LO
BATT
(low
battery)
input
(normally
high)
switches
low
when
the
low-battery
condition
is
sensed
(sce
"Low
Voltage,”
section
IV.4.C.
D.
This
causes
the
program
to
blink
ESP1.MAN/February 1992
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