User`s guide

Operation Theory
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4.1.3.3 Trigger Modes
DAQ-2213/2214 provides 3 trigger sources (internal software, external
analog, and digital trigger sources). Only 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).
There are 4 trigger modes (pre-trigger, post-trigger, middle-trigger, and
delay-trigger) working with the 4 trigger sources to initiate different scan
data acquisition timing when a trigger event occurs. For information of
trigger sources, please refer to section 4.5.
Pre-Trigger Acquisition
Use pre-trigger acquisition in applications to collect data before a trigger
event. The A/D starts when the specified function calls are executed to
begin the operation, and it stops when the external trigger event occurs.
Users must program the value M in
M_counter
(16bit) to specify the
amount of stored scanned data before the trigger event. If an external
trigger occurs after M scans of data are converted, the program only stores
the last M scans of data, as illustrated in Figure 12, where M_counter = M
=3, NumChan_counter =4, PSC_counter = 0. The total stored amount of
data = NumChan_counter *M_counter =12.
A
cquisition_in_progress
Scan_start
A
D_conversion
Scan_in_progress
(
SSHOUT
)(pin8 on CN2)
(M_counter = M = 3, NumChan_counter=4, PSC_counter=0)
Aq
uired data
A
cquired & stored data
(M scans)
O
p
eration start
Trigger
Figure 12: Pre-trigger (trigger occurs after M scans)