Start And Stop Trigger - National Instruments 653 Series User Manual

The mask for the pattern-matching trigger is the same as the one used for change
Note
detection. In other words, input lines significant for the pattern-matching trigger are also
significant for change detection.
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Start and Stop Trigger

When using a start and stop trigger, transfer starts upon receiving a trigger
on the start trigger line (ACK/STARTTRIG pin) and ends upon receiving
a trigger on the stop trigger line (STOPTRIG pin). A predetermined amount
of pretrigger and posttrigger data is saved in the buffer. If a stop trigger is
received before a start trigger, it is ignored. If the stop trigger arrives before
all the pretrigger data is acquired, NI-DAQ returns an error.
ACK (STARTTRIG)
STOPTRIG
REQ
Figure 2-18. Using a Start and Stop Trigger
Pattern-Matching Trigger
Instead of using an external signal on the start/stop trigger pins on the
I/O connector, you may start or stop (not both) an operation once a
user-specified digital pattern is matched.
Specify four parameters to set a pattern-matching trigger:
• Whether it is a start or stop trigger
• The data pattern to be detected/matched
• The mask, which selects the bits of interest for pattern detection
• Polarity (whether to detect data that matches or mismatches the
specified pattern)
The NI 653X immediately detects any occurrence of a specific pattern as
the data arrives. When a match occurs, the NI 653X starts acquiring data.
For example, if you want to start an acquisition when the two least
significant bits of your data are 1 and 0, you would specify your trigger
parameters to match those in Figure 2-19.
Pretrigger Data
2-31
Chapter 2 Using Your NI 653X
Posttrigger Data
NI 653X User Manual