ADLINK PCI-9820 - Manual (Page 31)

Operation Theory
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Use post-trigger acquisition when you want to collect data after the trigger
event, as illustrated in Fig 4.1.
Figure 4.1 Post trigger
4.3.2 Pre-trigger Acquisition
Use pre-trigger acquisition to collect data before the trigger event. The ac-
quisition starts once specified function calls are executed to begin the
pre-trigger operation, and it stops when the trigger event occurs.
If the trigger event occurs after the specified amount of data has been ac-
quired, the system only stores the data before the trigger event with the
specified amount, as illustrated in Fig 4.2.
Figure 4.2 Pre trigger (the trigger event occurs after the specified
amount of data has been acquired)
However, if the trigger event occurs before the specified amount of data has
been acquired, the system can either stop the acquisition immediately (which
implies the stored data will be less then the amount you specified) or ignore
the trigger signal until the specified amount of data has been acquired (which
assures the user can get the specified amount of data). These can be set by
software and are illustrated in Fig 4.3 and Fig 4.4.
Acquired & stored
data with the speci-
fied amount
Time
Trigger
event
Operation
start
Acquisition
stop
Acquired & stored
data with the speci-
fied amount
Time
Acquired data
Operation
start
Trigger
event