National Instruments DAQ X Series, Руководство пользователя

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Chapter 7 Counters
X Series User Manual 7-38 ni.com
With non-regeneration, old data will not be repeated. New data m u st be
contin u ally written to the b u ffer. If the program does not write new data to
the b u ffer at a fast eno u gh rate to keep u p with the generation, the b u ffer
will u nderflow and ca u se an error.
Continuous Buffered Sample Clocked Pulse Train
Generation
This f u nction generates a contin u o u s train of p u lses with variable idle and
active times. Instead of generating a set n u mber of data samples and
stopping, a contin u o u s generation contin u es u ntil yo u stop the operation.
Each point yo u write specifies p u lse specifications that are u pdated with
each sample clock. When a sample clock occ u rs, the c u rrent p u lse finishes
generation and the next p u lse u ses the next sample specifications.
Frequency Generation
Yo u can generate a freq u ency by u sing a co u nter in p u lse train generation
mode or by u sing the freq u ency generator circ u it, as described in the Using
the Frequency Generator section.
Using the Frequency Generator
The freq u ency generator can o u tp u t a sq u are wave at many different
freq u encies. The freq u ency generator is independent of the
fo u r general-p u rpose 32-bit co u nter/timer mod u les on X Series devices.
Fig u re 7-36 shows a block diagram of the freq u ency generator.
Figure 7-36. Frequency Generator Block Diagram
The freq u ency generator generates the Freq u ency O u tp u t signal. The
Freq u ency O u tp u t signal is the Freq u ency O u tp u t Timebase divided by a
n u mber yo u select from 1 to 16. The Freq u ency O u tp u t Timebase can be
100 kHz Time bas e
20 MHz Time bas e
Freq u ency
O u tp u t
Time bas e
FREQ OUT
Divi s or
(1–16)
Freq u ency Gener a tor
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