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Chapter 7 Counters
NI 6238/6239 User Manual 7-32 ni.com
Counter Triggering
Counters support three different triggering actions—arm start, start, and
pause.
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.
Start Trigger
For counter output operations, a start trigger can be configured 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.
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.