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Chapter 2 Function Reference — AO_Change_Parameter
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National Instruments Corporation 2-35 NI-DAQ FRM for PC Compatibles
PLL Reference Frequency
On some of the devices, you can phase-lock the internal timebase to an external reference
clock. The internal timebase can be an integral multiple of the external reference clock. This
feature is useful because you can synchronize the timebases of multiple devices so that they
are all locked to each other.
On DAQArb 5411 devices, you can phase-lock the internal timebase to a non-National
Instruments device using the I/O connector or to a National Instruments device using the RTSI
connector. You can select the reference clock source by using the
Select_Signal function
call. If the PLL reference clock source is the RTSI clock, set the reference clock frequency to
20 MHz.
To change the PLL reference frequency, set paramID to
ND_PLL_REF_FREQ.
Note
The values are set up in Hertz (Hz).
SYNC Duty Cycle
The SYNC output is a TTL version of the sine waveform being generated at the output. It is
obtained by using a zero-crossing detector on the sine output. It is generated on a separate
output connector instead of the main analog output connector. The SYNC output might not
carry any meaning for any other types of waveforms being generated.
You can vary the duty cycle of TTL output on the fly. To change the SYNC duty cycle as
the percentage of the time high, set paramID to
ND_SYNC_DUTY_CYCLE_HIGH
.
The
paramValue parameters imply percentage (%). To disable the SYNC output, set the
Table 2-13.
Parameter Setting Information for the Trigger Mode
Device Type
Per Channel
Selection Possible
Legal Range
for paramValue
Default Setting
for paramValue
DAQArb AT-5411
DAQArb PCI-5411
Yes
ND_SINGLE
ND_CONTINUOUS
ND_BURST
ND_STEPPED
ND_CONTINUOUS
Table 2-14.
Parameter Setting Information for PLL Reference Frequency
Device Type
Per Channel
Selection Possible
Legal Range
for
paramValue
Default Setting
for paramValue
DAQArb AT-5411
DAQArb PCI-5411
Yes 1,000,000,
10,000,000,
20,000,000
1,000,000