Tektronix 4000 Series, User Manual

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Trigger Setup
Untriggered display Triggered display
Trigger Modes
The trigger mode determines how the instrument behaves in the absence of a trigger event:
Normal trigger mode enables the instrument to acquire a waveform only when it is triggered. If no trigger occurs, the last
waveform record acquired remains on the display. If no last waveform exists, no waveform is displayed.
Auto trigger mode enables the instrument to acquire a waveform even if a trigger does not occur. Auto mode uses a timer that
starts when the acquisition is started, and the pretrigger information is obtained. If a trigger event is not detected before the
timer times out, the instrument forces a trigger. The length of time it waits for a trigger event depends on the time base setting.
118 Tektronix 4000 Series Oscilloscopes User Manual