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Triggering
Operating Basics
AC Line Voltage — this trigger source is useful when you are looking at
signals related to the power line frequency. Examples include devices
such as lighting equipment and power supplies. Because the digitizing
oscilloscope generates the trigger, you do not have to input a signal to
create the trigger.
Auxiliary Trigger — this trigger source is useful in digital design and
repair. For example, you might want to trigger with an external clock or
with a signal from another part of the circuit. To use the auxiliary trigger,
connect the external triggering signal to the Auxiliary Trigger input con-
nector on the oscilloscope rear panel (TDS 640A & TDS 644A only).
The digitizing oscilloscope provides three standard triggers for the main
trigger system: edge, pulse, and logic. Option 05 provides a video trigger. The
standard triggers are described in individual articles found in the
Reference
section
.
A brief definition of each type follows:
Edge — the “basic” trigger. You can use it with both analog and digital
test circuits. An edge trigger event occurs when the trigger
source
(the
signal the trigger circuit is monitoring) passes through a specified voltage
level
in the specified direction (the trigger
slope
).
Pulse — special trigger primarily used on digital circuits. Three classes of
pulse triggers are
width
,
runt,
and
glitch
. Pulse triggering is available on
the main trigger only.
Logic — special trigger primarily used on digital logic circuits. You select
Boolean operators for the trigger sources. Triggering occurs when the
Boolean conditions are satisfied. There are two kinds of logic triggers,
state
and
pattern.
(Logic triggers are available on the main trigger system
only.)
Video — (with option 05) special trigger used on video circuits. It helps
you investigate events that occur when a video signal generates a hori-
zontal or vertical sync pulse. Supported classes of video triggers include
NTSC
,
PAL
,
SECAM
, and high definition TV signals.
The trigger mode determines how the oscilloscope behaves in the absence of
a trigger event. The digitizing oscilloscope provides two different trigger
modes,
normal
and
automatic
.
Normal — this trigger mode lets the oscilloscope acquire a waveform
only when it is triggered. If no trigger occurs, the oscilloscope will not
acquire a waveform. (You can push FORCE TRIGGER to force the
oscilloscope to make a single acquisition.)
Types
Trigger Modes