Measurement Computing Data Translation DT3010 Series, Руководство пользователя, Страница: 119 / 232

Chapter 6
118
About-Trigger Acquisition
Use about-trigger acquisition mode when you want to acquire data both before and after a
specific external event occurs. This operation is equivalent to doing both a pre-trigger and a
post-trigger acquisition.
Using software, specify the following parameters:
• The dataflow as ContinuousPrePostTrigger.
• The pre-trigger source as Software.
• The post-trigger source as the external digital (TTL) trigger or the external analog
threshold trigger.
• If you are using triggered scan mode, the retrigger source as Software.
Refer to page 110 for more information on the supported conversion modes; refer to page 113
for information on the supported trigger sources.
Note: When using about-trigger acquisition, you cannot use an external retrigger in
triggered scan mode; refer to page 111 for more information on triggered scan mode.
The about-trigger acquisition starts when you start the operation. When the board detects the
selected post-trigger event, the board stops acquiring pre-trigger data and starts acquiring
post-trigger data.
If you are using software-retriggered scan mode and the post-trigger event has not occurred,
the board continues to acquire pre-trigger data using the Triggered Scan Counter to clock the
operation. If, however, the post-trigger event has occurred, the board continues to acquire
post-trigger data using the Triggered Scan Counter to clock the operation.
The about-trigger operation stops when the specified number of post-trigger samples has
been acquired or when you stop the operation. Refer to
page 111 for more information on
software-retriggered scan mode.
Figure 61 illustrates continuous about-trigger mode using a channel list of two entries:
channel 0 and channel 1. In this example, pre-trigger analog input data is acquired on each
clock pulse of the A/D sample clock, scanning the channel list continuously, until the
post-trigger event occurs. When the post-trigger event occurs, post-trigger analog input data
is acquired continuously on each clock pulse of the A/D sample clock.