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Chapter 5
Counters
Routing Frequency Output to a Terminal
You can route Frequency Output to any PFI terminal.
Default Counter/Timer Routing
Counter/timer signals are available to parallel digital I/O C Series modules. To determine the
signal routing options for modules installed in your system, refer to the
Device Routes
tab
in MAX.
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 Help
for more information about how to connect your signals for common counter
measurements and generations. Refer to
Physical Channels
in the
NI-DAQmx Help
or the
LabVIEW Help
for a list of default PFI lines for counter functions.
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.
