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Functional Description
The about trigger is always an external digital trigger. If you specify an
about trigger, the operation stops when a specified number of samples has
been acquired after the occurrence of the about-trigger event. As
described in the following sections, the availability of the about trigger
provides the capability to define operations that acquire data before a
trigger event (pre-trigger acquisition), operations that acquire data about
(before and after) a trigger event, and operations that acquire data after a
trigger event (post-trigger acquisition).
Pre-Trigger Acquisition
In pre-trigger acquisition, the data of interest appears before a specific
digital trigger event. Acquisition starts on an internal, external analog, or
external digital trigger event and continues until the digital trigger event.
Pre-trigger acquisition is available with DMA-mode operations only.
About-Trigger Acquisition
In about-trigger acquisition, the data of interest appears both before and
after a specific digital trigger event. Acquisition starts on an internal,
external analog, or external digital trigger event and continues until a
specified number of samples has been acquired after the digital trigger
event. About-trigger acquisition is available with DMA-mode operations
only.
Post-Trigger Acquisition
In post-trigger acquisition, the data of interest appears after a specific
event. Acquisition starts on an internal, external analog, or external digital
trigger event and continues until a specified number of samples has been
acquired or until the operation is stopped by software.
Gates
A gate allows conversions to proceed while in the active state. (The active
state is software-selectable.) Connect the external gate to TGIN (pin 46 of
the main I/O connector or pin 42 of STA-1800U connectors J1 and J2).
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