60
Choosing the right trigger mode and setting it up correctly can take some practice and it is best
done if you know something about the signal you are trying to capture. The oscilloscope provides
a variety of triggering types and logical conditions for generating a trigger event, such as Edge,
Slope, Pulse, Video, Window, Interval, Dropout, Runt, Pattern and Serial triggering. These
triggering types will be discussed in the following sections.
5.4
Trigger Source
The trigger source is the signal that will be compared to the logical conditions you set to generate
a trigger event. The most common trigger source is the signal on one of the analog input channels,
but the EXT BNC connector on the front panel can be used to trigger on an external signal. If you
are looking at waveforms that are derived from the AC line power, you'll probably want to use
the AC line as the trigger source. For example, to measure the 120 Hz ripple in a voltage regulator
circuit, you'd want to trigger on the 60 Hz AC line for a stable signal.
Press the Setup button in the Trigger section on the front panel to enter the TRIGGER menu.
Press the Source softkey and then turn the Universal Knob to select the desired trigger source.
The current trigger source is displayed at the upper right corner of the screen.
The edge trigger type allows triggering from the analog channels, an external signal on the EXT
input terminal, or the AC line. The remaining triggering types use only the analog channels as
their source.
If you select the Serial trigger type, the Source softkey changes to the Protocol softkey.
For the analog and external triggers, the trigger level can be set from -4 to 4 screen divisions.
5.5
Trigger Mode
The three trigger modes are Auto, Normal and Single.
After the oscilloscope begins to capture data, the oscilloscope operates by first filling the pre-
trigger buffer. The oscilloscope starts searching for a trigger after the pre-trigger buffer is filled
and data continues to flow through this buffer while it searches for the trigger. While searching
for the trigger, the oscilloscope overflows the pre-trigger buffer and the first data put into the
buffer is pushed out.
Figure 43 - Acquisition Memory Schematic
