HP 54540 Series - Page 86

Figure 5-1
Trigger
Trigger Basics
Trigger Basics
A trigger event is defined as an edge of a selected slope (either positive or
negative) that transitions through a selected voltage (trigger level). This is
referred to as the edge trigger mode. Events leading up to the trigger event
are referred to as occurring in negative time, and events that occur after the
rigger event are referred to as occurring in positive time. No matter what
mode the trigger circuit is in, a valid trigger is always caused by an edge.
Additional trigger features are added, like logic triggering and holdoff, that
allow you to further qualify the trigger event. The logic trigger modes are
pattern, state, delay by time, and delay by events. Basically you can think of
he logic trigger features as adding a 3- or 4-bit logic analyzer to your
oscilloscope. The edge trigger mode looks at only one channel, while logic
riggering allows you to qualify the trigger across all of the available trigger
sources, Rather than clutter up the waveform record with useless data that
you have to sift through, you can use logic triggering to pick out the area of
he signal you are most interested in viewing. Then, you can use time base
delay to view what happened before and after the trigger event.
The trigger circuit and sampler circuit operate in parallel. The sampler
samples the input signal at a specific rate. The trigger circuit operates
independently of the sampler circuit, and a trigger event does not have to
occur at the same time as a sample point. Because the oscilloscope knows
when the trigger event happened in relation to the sampled data, the
oscilloscope knows where to place the sampled data on the display.
ae "*igger
U mode s ony}
paaaues
5-3