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Chapter 2 Function Reference — GPCTR_Set_Application
NI-DAQ FRM for PC Compatibles 2-224
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National Instruments Corporation
Figure 2-17.
Single Triggered Pulse Width Generation Measurement
Use the GPCTR_Watch function with entityID = ND_COUNT_AVAILABLE to monitor the
progress of the counting process. This measurement completes when entityValue becomes
ND_YES. After this is completed, you can retrieve the counted value by using GPCTR_Watch
with entityID =
ND_COUNT, as shown in the following example code:
Create u32 variable count_available.
Create u32 variable counted_value.
repeat
{
GPCTR_Watch(deviceNumber, gpctrNumber, ND_COUNT_AVAILABLE,
count_available)
}
until (count_available = ND_YES)
GPCTR_Watch(deviceNumber, gpctrNumber, ND_COUNT, counted_value)
To calculate the measured interval, multiply the counted value by the period corresponding to
the timebase you are using. For example, if your
ND_SOURCE is ND_INTERNAL_20_MHZ, the
interval will be 1/(20 MHz) = 50 ns. If the
ND_COUNT is 4 (Figure 2-15), the actual interval is
4 * 50 ns = 200 ns.
Note The measured interval will correspond to the most recent pulse that arrived prior
to the invoking of
GPCTR_Watch
call with entityID set to ND_COUNT_AVAILABLE.
Caution There should be source transitions between gate transitions in order for this
measurement to be correct.
00
NO
NO
0
Gate
Source
Count
Count
Available
Measured
Interval
NO YES
0
0
1
22
Trigger
!