Operating instructions
Theory
of
Operation-71380
NORMAL
MODE
.
The
NORM
MODE
is
provided
when
U220-pin
12
is
LO
.
In
the
NORM
MODE,
only an
appro-
priate
trigger
signal
can
initiate
a
sweep
gate to
the
Sweep
Generator
(diagram
4)
.
Sweep
Control
integrated
circuit
U220
controls
sweep
lockout
and
hold
off
functions
.
AUTOMODE
.
The
Auto
Control
stage
produces
a
free-
running
reference
trace
(bright
base
line) in
the
absence
of
a
trigger
signal
.
A
HI
level
from
MODE
switch
S230
is
inverted
by
Q230
to
U220-pin 19
LO,
which
selects
AUTOMODE
operation
.
In
the
presence
of
a
trigger
pulse
from
the
Trigger
Generator
(diagram
2),
a
HI
level at
U220-pin
1
discharges
the
auto
stage
which
inhibits
the
auto
sense
signal
from
U220-pin
3
.
In
the
absence
of
a
trigger
pulse,
the
LO
level
at
U220-pin
1
an
auto
sense
signal
is
initiated
from
U220-pin 3
to
the
Trigger
Generator
(diagram
2)
.
SINGLE
SWEEP
MODE
.
SINGLE
SWEEP
operation
pro-
vides
display
of
only
one
sweep
.
After
one
sweep
has
run,
all
othersweepsare
inhibited
until
the
SINGLESWP-RESET
push
button
is
pressed
.
The
READY
light
indicates
when
the
sweep
is
ready
to
accept
a
trigger
.
3-
1
0
Fig
.
3-5
.
Detailed
block
diagram
of
Logic
circuit
.
After
completion
of
one
sweep,
the
hold
off
start
pulse
at
U220-pin
16
causes
the
sweep
disable
out
at
pin
17 to
rise
HI
.
A
HI
level at
U220-pin
12
initiates
single
sweep
opera-
tion
and
holds
the
sweep
disable
out
at
U220-pin
17 HI
after
completion
of
the
sweep
.
Momentary
contact
of
the
RESET
push
button
places
a
LO
at
U220-pins
14 and
15,
which
removes
the
sweep
disable
out
from
pin
17
and
allows
the
Sweep
Generator
(diagram
4) to
accept
a
trigger
.
Interface
connector
1315
provides
a
remote
single-sweep
re-
set
input
from
compatible
mainframes
.
Hold
Off Timing
The
hold
off
stages
prevent
the
Sweep
Generator
(diagram
4)
from
being
retriggered
until
the
sweep
timing
capacitors
are
discharged
.
At
the
end
of
each
sawtooth
waveform
from
the
Sweep
Generator
(diagram
4),
a
sweep
stop
comparator
pulse
(H
I)
is
coupled
to
U220-pin
16
.
This
pulse
enables
the
hold
off
timing
circuits
at
U220-pin
8,
which
sets
the
sweep
disable
out
at
U220-pin
17
HI and
the
hold
off
signal at
pin
10
LO
for
the
duration
of the
hold
off
cycle
.
Hold
off
timing
(U220-pin
8)
is
provided
by
capacitors
C212
through
C215,
and
resistors
R212
through
R214
.
Transistors
Q203
and
TIME/DIV
TRIG'D
C
1986-64