National Instruments 653X - Manual (Page 47)

Chapter 2 Using Your 653X
© National Instruments Corporation 2-29 653X User Manual
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
Note The mask for the pattern-matching trigger is the same as the one used for change
detection. In other words, input lines significant for the pattern-matching trigger are also
significant for change detection.
• Polarity (whether to detect data that matches or mismatches the
specified pattern)
The 653X device detects any occurrence of a specific pattern immediately
as the data comes in. When a match occurs, the 653X device 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.
REQ
STOPTRIG
ACK (STARTTRIG)
Pretrigger Data Posttrigger Data