Counter Triggering; Other Counter Features; Cascading Counters - National Instruments X Series 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. 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—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.

Other Counter Features

The following sections list the other counter features available on X Series devices.

Cascading Counters

You can internally route the Counter n Internal Output and Counter n TC signals of each counter
to the Gate inputs of the other counter. By cascading two counters together, you can effectively
create a 64-bit counter. By cascading counters, you can also enable other applications. For
example, to improve the accuracy of frequency measurements, use reciprocal frequency
measurement, as described in the Large Range of Frequencies with Two Counters
X Series User Manual
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