176 Keysight InfiniiVision 3000 X-Series Oscilloscopes User's Guide11 Trigger Mode/CouplingTo select the Auto or Normal trigger modeWhen the oscilloscope is running, the trigger mode tells the oscilloscope what todo when triggers are not occurring.In the Auto trigger mode (the default setting), if the specified trigger conditions arenot found, triggers are forced and acquisitions are made so that signal activity isdisplayed on the oscilloscope.In the Normal trigger mode, triggers and acquisitions only occur when thespecified trigger conditions are found.To select the trigger mode:1 Press the [Mode/Coupling] key.2 In the Trigger Mode and Coupling Menu, press the Mode softkey; then selecteither Auto or Normal.See the following "When to Use Auto Trigger Mode" on page 177 and "Whento Use Normal Trigger Mode" on page 177 descriptions.You can also configure the [Quick Action] key to toggle between the Auto andNormal trigger modes. See "Configuring the [Quick Action] Key" on page 307.Triggering and thePre- andPost-TriggerBuffersAfter the oscilloscope starts running (after pressing [Run] or [Single] or changingthe trigger condition), the oscilloscope first fills the pre-trigger buffer. Then, afterthe pre-trigger buffer is filled, the oscilloscope starts searching for a trigger, andsampled data continues to flow data through the pre-trigger buffer in a first-infirst-out (FIFO) manner.When a trigger is found, the pre-trigger buffer contains the events that occurredjust before the trigger. Then, the oscilloscope fills the post-trigger buffer anddisplays the acquisition memory. If the acquisition was initiated by [Run/Stop], theprocess repeats. If the acquisition was initiated by pressing [Single], the acquisitionstops (and you can Pan and Zoom the waveform).In either Auto or Normal trigger mode, a trigger may be missed if the event occurswhile the pre-trigger buffer is being filled. This may be more likely, for example,when the horizontal scale knob is set to a slow time/div setting, such as500 ms/div.Trigger Indicator The trigger indicator at the top right of the display shows whether triggers areoccurring.In the Auto trigger mode, the trigger indicator can show:
