Operating instructions

Theory of Operation--7887
Auto
Mode
Single Sweep
Mode
3- 6
AUTOMODE
OPERATION
WITH
TRIGGER SIGNAL
The Auto
Control stage
produces a free-running
reference
trace (bright base
line) in the absence
of a
trigger
signal .
A high level from
MODE switch S230
is inverted by
Q230
to set U220
pin 19 low, which
selects AUTO
MODE
operation .
In the presence of
a trigger pulse from
the Trigger
Generator (diagram 2),
a high 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
low level at U220
pin 1 enables the Auto
Control stage .
After a time
delay determined by
R228,
C228,
and circuitry
internal to U220 pin
6, an Auto
Sense
signal is initiated
from U220 pin 3 to the
Trigger
Generator
(diagram 2) .
Single Sweep
operation provides
display of only one
sweep .
After one sweep has
run the sweep is inhibited
until
the SINGLE SWP
RESET button is pressed
. The
READY light indicates
that the sweep is ready
to accept a
trigger .
AUTO MODE OPERATION
WITHOUT TRIGGER
SIGNAL
HOLD
OFF TIMING
Figure 3-3 . Timing diagram
for Gate Generator stage
(Q92, Q96, Q98) .
After
completion of one
sweep, the Holdoff
Start pulse at
U220
pin 16 causes the
Swp Disable Out
at pin 17 to rise
high .
A high level at
U220 pin 12 initiates single
sweep
operation and holds
the sweep disable
out at U220 pin
17 after completion
of the sweep .
Momentary contact of
the RESET
push button places
a low 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 B15 provides a
remote
Single-Sweep
Reset input
from compatible
mainframes .
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 Holdoff
Start pulse (high) 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 high
and the Hold Off signal
at pin 10 low
for the duration of
the hold-off cycle .
Hold-
off timing
(U220 pin 8) is
provided by capacitors
C211
through
C215, and
resistors R212 through
R214 .
Transistors Q203 and
0204 prevent the
Swp Disable Out