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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-103x 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,

Specifications 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.

National Instruments PXI-6683 Series User Manual

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