User manual

31 Chapter 4
4.2.5 About Trigger Acquisition Mode
Use about-trigger acquisition mode when you want to acquire data both
before and after a specific trigger event occurs. This operation is equiva-
lent to doing both a pre-trigger and a post-trigger acquisition. When using
software, please specify the following parameters after About-Trigger
Acquisition Mode has been set.
• The sample clock source and sample rate
• The trigger source
• The total acquired sample number N
• The specific sample number M after the trigger event. The range of pre-
set sample number is from 2 to 65536 samples.
In about-trigger mode, users must first designate the size of the allocated
memory and the amount of samples to be snatched after the trigger event
happens. The about-trigger acquisition starts when the first clock signal
comes in. Once a trigger event happens, the on-going data acquisition
will continue until the designated amount of samples have been reached.
When the PCIE-1744 detects the selected about trigger event, the card
keeps acquiring the preset number of samples, and keeps the total number
of samples on the FIFO.
Figure 4.3: About-Trigger Acquisition Mode