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NI PXI-6683 Series User Manual
The NI PXI-6683 has the capability to discipline its 10 MHz TCXO to an external time reference
(such as GPS, IEEE 1588, or IRIG-B) by monitoring and adjusting the clock relative to the
external time reference. The driver software automatically disciplines the TCXO to the selected
time reference. TCXO disciplining can be disabled by setting the time reference to
Free
Running
.
Note
Some chassis (including the NI PXI-103
x
series) require toggling a hardware
switch to enable the system timing module to override PXI_CLK10. Refer to your
chassis user manual for more information.
Time-Synchronized Clock and Event Generation
The NI PXI-6683 Series is capable of generating clock signals and triggers based on the
synchronized time base. The NI PXI-6683 Series keeps an internal time base with 10 ns
resolution that can be free running or synchronized to GPS, IEEE 1588, IRIG-B, or PPS. The
NI Sync API allows you to schedule triggers to occur at an arbitrary future time (future time
events), or clocks with high and low times that are multiples of 10 ns
(refer to Appendix A,
for information about limitations). It is also possible to program the start and end
time of a clock generated in this way.
Refer to Table 3-6 for a list of destinations for synchronized time clocks and future-time events.
PXI_CLK10 Synchronization Design Recommendations
•
Minimize Starting/Stopping of PXI_CLK10 Disciplining
—From startup, the
PXI_CLK10 synchronization can take on the order of minutes to stabilize to the time
reference. You should design your application such that PXI_CLK10 disciplining runs
asynchronous to other programs that might start and stop more frequently. This minimizes
the time spent letting the synchronization stabilize and lock.
•
Avoid Disrupting PXI_CLK10 Disciplining
—While you can use the devices used for
PXI_CLK10 disciplining within other applications, you should avoid resetting them or
changing the configured time reference. Doing so disrupts the PXI_CLK10 disciplining
process.
Routing Signals
The NI PXI-6683 Series has versatile trigger routing capabilities. It can route signals to and from
the front panel, the PXI star triggers, and the PXI triggers. In addition, the polarity of the
destination signal can be inverted, which is useful when handling active-low digital signals.
The NI PXI-6683 can replace the PXI backplane's native 10 MHz clock (PXI_CLK10) with its
high-stability TCXO, or with a 10 MHz clock signal from the CLKIN connector (replacing
PXI_CLK10 is not supported by the NI PXI-6683H). The NI PXI-6683 Series can route the
TCXO, or PXI 10 MHz reference clock to CLKOUT.