National Instruments USB-621 Series, User Manual

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Chapter 8 Counters
NI USB-621x User Manual 8-24 ni.com
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 8-25 shows a contin u o u s p u lse train generation ( u sing the rising
edge of So u rce).
Figure 8-25. 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.
Finite Pulse Train Generation
This f u nction generates a train of p u lses of predetermined d u ration. This
co u nter operation req u ires both co u nters. The first co u nter (for this
example, Co u nter 0) generates a p u lse of desired width. The second
co u nter, Co u nter 1, generates the p u lse train, which is gated by the p u lse of
the first co u nter. The ro u ting is done internally. Fig u re 8-26 shows an
example finite p u lse train timing diagram.
Figure 8-26. Finite Pulse Train Timing Diagram
S OURCE
OUT
Co u nter Armed
Co u nter 0
(P a ired Co u nter)
Co u nter 1
Gener a tion
Complete