National Instruments NI USB-621x - Manual (Page 111)

Chapter 9 Counters
© National Instruments Corporation 9-31 NI USB-621x User Manual
You can use these defaults or select other sources and destinations for the
counter/timer signals in NI-DAQmx. Refer to Connecting Counter Signals
in the NI-DAQmx Help or the LabVIEW 8.x Help for more information
about how to connect your signals for common counter measurements and
generations. M Series default PFI lines for counter functions are listed in
Physical Channels in the NI-DAQmx Help or the LabVIEW 8.x Help.
Counter Triggering
Counters support three different triggering actions—arm start, start, and
pause.
Arm Start Trigger
Any counter operation can use the arm start trigger.
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