National Instruments Data Acquisition Device NI USB-621x, User Manual

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Chapter 8 Counters
NI USB-621x User Manual 8-22 ni.com
Pulse Train Generation
Continuous Pulse Train Generation
This f u nction generates a train of p u lses with programmable freq u ency and
d u ty cycle. The p u lses appear on the Co u nter n Internal O u tp u t signal of the
co u nter.
Yo u can specify a delay from when the co u nter is armed to the beginning
of the p u lse train. The delay is meas u red in terms of a n u mber of active
edges of the So u rce inp u t.
Yo u specify the high and low p u lse widths of the o u tp u t signal. The p u lse
widths are also meas u red in terms of a n u mber of active edges of the So u rce
inp u t. Yo u also can specify the active edge of the So u rce inp u t (rising or
falling).
The co u nter can begin the p u lse train generation as soon as the co u nter is
armed, or in response to a hardware start trigger. Yo u can ro u te the Start
Trigger to the Gate inp u t of the co u nter.
Yo u also can u se the Gate inp u t of the co u nter as a Pa u se Trigger (if it is not
u sed as a Start Trigger). The co u nter pa u ses p u lse generation when the
Pa u se Trigger is active.
Fig u re 8-24 shows a contin u o u s p u lse train generation ( u sing the rising
edge of So u rce).
Figure 8-24. Continuous Pulse Train Generation
Contin u o u s p u lse train generation is sometimes called freq u ency division.
If the high and low p u lse widths of the o u tp u t signal are M and N periods,
then the freq u ency of the Co u nter n Internal O u tp u t signal is eq u al to the
freq u ency of the So u rce inp u t divided by M + N .
For information abo u t connecting co u nter signals, refer to the Default
Counter/Timer Pinouts section.
S OURCE
OUT
Co u nter Armed