3-4
Triggering the Oscilloscope
To select a trigger mode: Normal, Auto, Auto Level
To select a trigger mode: Normal, Auto, Auto Level
1Press the Mode/Coupling key.

2Press the

Mode softkey, then select Normal, Auto, or Auto Level mode.
•Normal mode displays a waveform when the trigger conditions are met,
otherwise the oscilloscope does not trigger and the display i s not updated.
•Auto mode is the same as Normal mode, except it forces the oscillo scope to
trigger if the trigger conditions are not met.
•Auto Level mode (54620-series only) works only when edge triggering on
analog channels or external trigger. The o scilloscope first tries to Normal
trigger. If no trigger is found, it searches for a signal at least 10% of full scale
on the trigger s ource and sets t he trigger lev el to the 50% am plitude point.
If there is still no signal present, the oscil loscope auto triggers. This mode
is useful when moving a probe from point to point on a circuit board.
Auto Level and Auto modes
Use th e a ut o tr ig ge r m od e s f or si gn al s ot he r t ha n lo w- re pe ti t iv e- ra te si g na ls an d
for unknown signal levels. To display a dc signal, you must use one of these two
auto trigger modes since there are no edg es on which to trigger.
Auto Level mode (54620-series only) is the same as Auto mode with a n
automatic trigger level adjustment. The oscilloscope looks at the level on the
signals, and if the trigger level is out-of-range with respect to the signal, the
scope adjusts the trigger level back to the middle of the signal.
When you select Run, the oscilloscope operates by first filling the pre-trigger
buffer. It starts searching for a trigger after the pre-trigge r buffer is filled, and
continues to flow data through this buffer while it searches for the trigger. While
searching for t he trigger, the os cilloscope ov erflows the pre -trigger buff er; the
first data put into the buffer is the first push ed out (FIFO). When a trigger is
found, the pre-trigger buffer will contain the e vents that occurred just before
the trigger. If no trigger is found, the oscilloscope generates a trigger and
displays the data as though a trigger had occurred.
When you select Single, the oscilloscope will fill pre-trigger buffer memory, and
continue flowing data through the pre-trigger buffer until the auto trigger
overrides the searching and forces a trigger. At the end of the trace, the scope
will stop and display the results.