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HDO9000 High Definition Oscilloscopes Operator's Manual
Trigger
Triggers define the event around which digitized information is displayed on the oscilloscope touch
screen.
Different
Trigger Types
are used to select different events in the trigger source waveforms: edge
voltages, pulse widths, high/low states, etc. These may be a single channel event or a complex
pattern of events across several channels. On instruments with Mixed Signal capabilities, many
triggers can be set on either analog channels, including the External Trigger input, or digital lines.
In addition to the type, the
Trigger Mode
determines how the instrument behaves as it encounters
trigger events: take a single acquisition and stop, holding on to the display of the last acquisition, or
continuously take and display acquisitions.
In both cases, when the previous acquisition has completed processing, the oscilloscope is again
ready to acquire and the READY indicator is lit. If, while READY, the trigger circuit detects a signal
that matches the trigger conditions, the oscilloscope triggers on the next matching event, and the
TRIG'D indicator is lit.
Unless modified by a pre- or post-trigger Delay, the trigger event appears at time 0 at the horizontal
center of the grid, and a period of time equal to five divisions of the timebase is shown to the left and
right of it. Delay shifts the trigger position on screen, displaying a different portion of the pre- or post-
trigger waveform.
An additional condition of
Holdoff
by time or events is available for Edge and Pattern triggers,
including those that appear within MultiStage triggers. Holdoff arms the trigger on the first matching
event, inserts the holdoff count, then triggers on a subsequent event. Often, especially with repetitive
signals, the initial arming event appears to the left of the trigger in "negative" acquisition time.
Trigger Modes
The Trigger Mode determines how often the instrument acquires. It is equivalent to how analog
oscilloscopes "sweep," or refresh, the display. Trigger Mode can be set from the Trigger menu or from
the front panel Trigger control group.
In Single mode, when you choose Trigger > Single or press the front panel Single button, the
oscilloscope readies, arms, and triggers provided all trigger conditions (including Holdoff) are met. It
then stops and continues to display the last acquisition until a new one is taken. The oscilloscope
remains armed unless manually stopped or triggered, and if a valid trigger does not occur, invoking
Single a second time will force a trigger and display the acquisition.
In Normal mode, operation is the same as in Single, except that the trigger automatically re-arms
after the previous acquisition is complete, and data is continuously refreshed on the touch screen.
Auto operates the same as Normal mode, except that a trigger is forced if the trigger event has not
occurred within a preset timeout period.
Stop ceases acquisition processing until you select one of the other three modes. The arming and
Holdoff counters are cleared, even if there has not yet been a trigger since the previous acquisition.
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