Circuit Description-465
signal
at
the
collector
of
0862
is
connected
to
the
AZ
Axis
Gate Circuit
to
control
CRT
blanking and
to
generate
the
+
A GATE signal. The signal
at
the
collector
of
0864
is
connected
to
the
emitter
of
the
Sweep Disconnect Ampli-
fier stage
(01024)
in
the
A Sweep Generator Circuit
to
initiate A Sweep generation.
B Sweep Gate
0812
and
0814
compose
the
B Sweep Gate Circuit.
They also form an
emitter-coupled
stage where only
one
transistor can be
conducting
at
any
time. The
input
signal
to
the
stage
is
the
positive-going trigger signal from
the
B
Fire Trigger TD
in
the
B Trigger Generator Circuit.
The
signal
at
the
collector
of
0812
is
connected
to
the
B Z Axis
Gate Circuit
to
control
CRT
blanking and
to
generate
the+
B GATE signal. The signal
at
the
collector of
0814
is
connected
to
the
emitter
of
the
Sweep Disconnect Ampli-
fier stage
(01084)
in
the
B Sweep Generator Circuit
to
initiate B Sweep generation.
Sweep Control Integrated Circuit
U870
is
the
Sweep Control Integrated Circuit. Several
functions are
performed
in this stage, depending on
the
mode
of
operation
of
the
instrument
sweep generators. The
following
is
a brief
explanation
of
the
function associated
with each pin
of
the
IC.
Pin
1.
This
is
the
positive
Auto
Sense input. The signal
connected
here comes from
the
A Fire Trigger TD.
Pin 2. This
is
the
negative
Auto
Sense
input.
A fixed
DC
level established by R871
and
R872
is
connected
here.
Pin
3. This
is
the
+
auto
gate terminal.
In
the
AUTO
mode
of
operation,
if
no
trigger signals are applied
to
pin 1
of
U870 during
the
~100
ms following
the
end
of
holdoff
the
gate level
at
pin 3 steps
LO
to
turn
0864
on
which
initiates a sweep.
Pin
4. Not used in this application.
Pin
5.
Input
terminal for negative voltage supply.
Pin 6. This
is
the
auto
gate timing terminal.
R879
and
C879
determine
the
amount
of
time
between
the
end
of
holdoff
and
the
generation
of
the
auto
gate.
3-12
'•.
::
.
~-
Pin
7.
This terminal lights
the
TRIG'D
light when a
triggered gate has
occurred.
Pin
8. This
is
the
holdoff
timing terminal. The R/C
connected
to
this terminal (selected by
the
TIME/DIV
switch) determines
the
length
of
holdoff
time.
Pin 9. Ground terminal.
Pin
10. This
is
the
Holdoff
output
terminal. The gate
level present here
is
LO
during sweep
holdoff
time and
HI
otherwise.
Pin 11. This terminal lights
the
READY light when
operating
in
the
single sweep
mode.
Pin
12. This
is
the
single sweep
mode
terminal. When +5
volts
is
applied
to
this terminal
the
sweep operates
in
the
single sweep
mode;
when
the
terminal
is
left open or
grounded
the
sweep
operates
in
the
repetitive mode.
Pin
13. Not used
in
this application.
Pins 14 & 15. Single sweep reset terminals. Pushing
the
PUSH TO RESET
button
prepares
the
single sweep
circuitry
to
respond
to
the
next
one
triggering event. Also
causes
the
READY light
to
be lit.
Pin 16. This
is
the
holdoff
start
input
terminal. The
HI
sweep reset gate pulse from
the
sweep generators
is
applied
here
to
initiate sweep
holdoff.
Pin
17. This
is
the
sweep disable
output
terminal. The
gate level
at
this terminal
is
HI
during holdoff and
LO
otherwise.
Pin
18. Sweep
lockout
input.
+5 volts applied
to
this
terminal disables all sweep
action.
Pin
19.
Auto
mode
terminal. Grounding this terminal
enables
auto
sweep
operation.
Pin
20.
Input
terminal
for
positive voltage supply.
®I
C
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