© National Instruments
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6-3
cDAQ-9185/9189 User Manual
Counter Triggering
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 or a specific time. 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 it 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
—You can use the start trigger for counter output functions. You can
configure a start trigger to begin a finite or continuous pulse generation. After 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. Possible triggers for counter output operations are a hardware signal
or a specific time.
For counter input functions, you 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.
Counter Input Applications
The following sections list the various counter input applications available on the cDAQ chassis:
•
Counting Edges
•
Pulse-Width Measurement
•
Pulse Measurement
•
Semi-Period Measurement
•
Frequency Measurement
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