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Chapter 2 Function Reference — GPCTR_Set_Application
NI-DAQ FRM for PC Compatibles 2-238
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National Instruments Corporation
6602 and 455X devices with counter width 32 bits, you can generate pulses with a delay and
length between 100 ns and 214 s long.
Figure 2-25.
Buffered Period Measurement
Typically, you will find modifying the following parameters through the
GPCTR_Change_Parameter function useful when the counter application is
ND_BUFFERED_PERIOD_MSR. You can change the following:
•
ND_SOURCE to ND_INTERNAL_100_KHZ. With this timebase, you can measure intervals
between 20 µs and 160 s long. The resolution will be lower than if you are using
ND_INTERNAL_20_MHZ timebase.
•
ND_SOURCE_POLARITY to ND_HIGH_TO_LOW
•
ND_GATE to any legal value listed in the GPCTR_Change_Parameter function
description
•
ND_GATE_POLARITY to ND_NEGATIVE. Measurements will be performed between
successive high-to-low transitions of the signal present at the gate.
To provide your timebase, you can connect your timebase source to one of the PFI pins on the
I/O connector and change
ND_SOURCE and ND_SOURCE_POLARITY to the appropriate values.
You also can configure the other general-purpose counter for
ND_PULSE_TRAIN_GNR, and set
ND_SOURCE of this counter to ND_OTHER_GPCTR_TC to measure intervals longer than 160 s.
Note The counter will start counting as soon as you arm it. Be aware of this when you
interpret the first count in your buffer.
Caution If gate edges arrive and no source edges are present between those gate edges, then
the previously saved value is saved again as shown in Figure 2-25. Please make
sure that this condition does not occur during your measurement.
Source
Gate
Buffer
21436517325416324
Measured
Period
Measured
Period
Measured
Period
7 7
6
7
6
4
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