ADLINK DAQe-2006 - Manual (Page 49)

Operation Theory 37
Trigger Modes
The DAQ-/DAQe-/PXI-2016/2010/2006/2005 card provides four
trigger sources (internal software trigger, external analog trigger,
external digital trigger, and SSI trigger signals). You must select
one of them as the source of the trigger event. A trigger event
occurs when the specified condition is detected on the selected
trigger source. For example, a rising edge on the external digital
trigger input. Refer to section 4.6 for more information on SSI sig-
nals.
There are four trigger modes (pre-trigger, post-trigger, middle-trig-
ger, and delay-trigger) working with the four trigger sources to ini-
tiate different scan data acquisition timing when a trigger event
occurs. They are described in the following sections. For informa-
tion on trigger sources, refer to section 4.5.
Pre-Trigger Acquisition
Use pre-trigger acquisition in applications where you want to
collect data before a trigger event. The A/D starts to sample
when you execute the specified function calls to begin the pre-
trigger operation, and it stops when the trigger event occurs.
Users must program the value M in M_counter (16 bits) to
specify the amount of the stored scans before the trigger event.
If an external trigger occurs, the program only stores the last M
scans of data converted before the trigger event, as illustrated
in Figure 4-4, where M_counter = M =3, PSC_counter = 0. The
post scan count is 0 because there is no sampling after the trig-
ger event in pre-trigger acquisition. The total stored amount of
data = Number of enabled channels * M_counter.