National Instruments NI 6221, User Manual

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Chapter 7 Counters
© National Instruments Corporation 7-29 M Series User Manual
Counter n Up_Down Signal
Counter n Up_Down is another name for the Counter n B signal.
Counter n HW Arm Signal
The Counter n HW Arm signal enables a counter to begin an input or output
function.
To begin any counter input or output function, you must first enable, or arm,
the counter. In some applications, such as buffered semi-period
measurement, the counter begins counting when it is armed. In other
applications, such as single pulse-width measurement, the counter begins
waiting for the Gate signal when it is armed. Counter output operations can
use the arm signal in addition to a start trigger.
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.
Routing Signals to Counter n HW Arm Input
Any of the following signals can be routed to the Counter n HW Arm input.
• RTSI <0..7>
• PFI <0..15>
• ai/ReferenceTrigger
• ai/StartTrigger
• PXI_STAR
• Analog Comparison Event
Counter 1 Internal Output can be routed to Counter 0 HW Arm. Counter 0
Internal Output can be routed to Counter 1 HW Arm.
Some of these options may not be available in some driver software.
Counter n Internal Output and Counter n TC Signals
The Counter n Internal Output signal changes in response to Counter n TC.
The two software-selectable output options are pulse output on TC and
toggle output on TC. The output polarity is software-selectable for both
options.