HP 54540 Series - Page 91

Figure 5-4
Trigger
Edge Trigger Mode
Holdoff Softkey
The holdoff softkey disables the trigger circuit for a selectable time period
or for a number of events after the trigger event. Holdoff is selected in 20-ns
time increments from 40 ns to 320 ms, or by number of events from 2 to
16,000,000. Time and event are toggied with the knob. An events is a
pattern, state, or edge. The maximum event counting rate is 70 MHz.
You use holdoff to synchronize a waveform to a trigger signal. Holdoff is used
to stabilize the display of complex waveforms, or to trigger on a burst of
pulses that are separated by time. Figure 5-4 shows a pulse burst with the
holdoff time represented as T1. You may notice that holdoff keeps the trigger
circuit from rearming until after the pulse burst is over. That way, the first
pulse in the next burst is the trigger event.
The advantage of digital holdoff is that it is a fixed number. Asa result,
changing the time base settings does not affect holdoff and the oscilloscope
remains triggered. In contrast, the holdoff in analog oscilloscopes is a
function of the time base setting, making it necessary to readjust the holdoff
each time you change the time base setting. Also, there is no holdoff when
edge triggering using auxiliary or line trigger as the source.
5-8