Stop Trigger Modes; Pre-Triggering And Post-Triggering Modes - Measurement Computing PCI-2517 User Manual

PCI-2517 User's Guide Functional Details
Analog triggering
You can select any analog channel in the scan as the trigger channel. You can program the trigger level, the
rising or falling edge, and hysteresis.
Pattern triggering
You can select any scanned digital input channel pattern to trigger an acquisition, including the ability to mask
or ignore specific bits.
Counter triggering
You can program triggering to occur when one of the counters meets or exceeds a set value, or is within a range
of values. You can program any of the included counter channels as the trigger source.
Software-based triggering usually results in a long period of inactivity between the trigger condition being
detected and the data being acquired. However, the PCI-2517 avoids this situation by using pre-trigger data.
When software-based-triggering is used, and the PC detects the trigger condition—which may be thousands of
readings after the actual occurrence of the signal—the PCI-2517 driver automatically looks back to the location
in memory where the actual trigger-causing measurement occurred, and presents the acquired data that begins at
the point where the trigger-causing measurement occurs. The maximum inactive period in this mode equals one
scan period.
Set pre-trigger > 0 when using counter as trigger source
When using a counter for a trigger source, you should use a pre-trigger with a value of at least 1. Since all
counters start at zero with the first scan, there is no valid reference in regard to rising or falling edge. Setting a
pre-trigger to 1 or more ensures that a valid reference value is present, and that the first trigger will be
legitimate.

Stop trigger modes

You can use any of the software trigger modes explained previously to stop an acquisition.
For example, you can program an acquisition to begin on one event—such as a voltage level—and then stop on
another event—such as a digital pattern.

Pre-triggering and post-triggering modes

The PCI-2517 supports four modes of pre-triggering and post-triggering, providing a wide-variety of options to
accommodate any measurement requirement.
When using pre-trigger, you must use software-based triggering to initiate an acquisition.
No pre-trigger, post-trigger stop event
In this simple mode, data acquisition starts when the trigger is received, and the acquisition stops when the stop-
trigger event is received.
Fixed pre-trigger with post-trigger stop event
In this mode, you set the number of pre-trigger readings to acquire. The acquisition continues until a stop-
trigger event occurs.
No pre-trigger, infinite post-trigger
In this mode, no pre-trigger data is acquired. Instead, data is acquired beginning with the trigger event, and is
terminated when you issue a command to halt the acquisition.
Fixed pre-trigger with infinite post-trigger
You set the amount of pre-trigger data to acquire. Then, the system continues to acquire data until the program
issues a command to halt acquisition.
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