Counter Triggering - National Instruments Data Acquisition Device NI USB-621x User Manual

Counter Triggering

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Counters support three different triggering actions:
• Arm Start Trigger—To begin any counter input or output function,
you must first enable, or arm, the counter. Software can arm a counter
or configure counters to be armed on a hardware signal. Software calls
this hardware signal the Arm Start Trigger. Internally, software routes
the Arm Start Trigger to the Counter n HW Arm input of the counter.
For counter output operations, you can use the arm start trigger in
addition to the start and pause triggers. For counter input operations,
you can use the arm start trigger to have start trigger-like behavior. The
arm start trigger can be used for synchronizing multiple counter input
and output tasks.
When using an arm start trigger, the arm start trigger source is routed
to the Counter n HW Arm signal.
• Start Trigger—For counter output operations, a start trigger can be
configured to begin a finite or continuous pulse generation. Once a
continuous generation has triggered, the pulses continue to generate
until you stop the operation in software. For finite generations, the
specified number of pulses is generated and the generation stops unless
you use the retriggerable attribute. When you use this attribute,
subsequent start triggers cause the generation to restart.
When using a start trigger, the start trigger source is routed to the
Counter n Gate signal input of the counter.
Counter input operations can use the arm start trigger to have start
trigger-like behavior.
• Pause Trigger—You can use pause triggers in edge counting and
continuous pulse generation applications. For edge counting
acquisitions, the counter stops counting edges while the external
trigger signal is low and resumes when the signal goes high or vice
versa. For continuous pulse generations, the counter stops generating
pulses while the external trigger signal is low and resumes when the
signal goes high or vice versa.
When using a pause trigger, the pause trigger source is routed to the
Counter n Gate signal input of the counter.
8-31
Chapter 8 Counters
NI USB-621x User Manual