ADLINK PXI-2006 - Manual (Page 43)

Operation Theory 33
There are 4 trigger modes to start the scan acquisition, please
refer to section 4.1for more details. The data transfer mode is dis-
cussed below.
Note:
1. The maximum A/D sampling rate is 2MHz for DAQ/PXI-
2010, 500kHz for DAQ/PXI-2005, 250kHz for DAQ/PXI-
2006 and 800kHz for DAQ/PXI-2016. Therefore, the
minimum setting of SI_counter is 20 for DAQ/PXI-2010,
80 for DAQ/PXI-2005, 160 for DAQ/PXI-2006 and 50 for
DAQ/PXI-2016 while using the internal TIMEBASE.
2. The SI_counter is a 24-bit counter. Therefore, the maxi-
mum scan in-terval while using an internal TIMEBASE =
224/40M s = 0.419s.
Trigger Modes
DAQ/PXI-20XX provides 4 trigger sources (internal software trig-
ger, ex-ternal analog trigger, external digital trigger or 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). Please refer to section
4.6 for more information about SSI signals.
There are 4 trigger modes (pre-trigger, post-trigger, middle-trigger,
and delay-trigger) working with the 4 trigger sources to initiate dif-
ferent scan data acquisition timing when a trigger event occurs.
They are described as follows. For information of trigger sources,
please 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