NI 5411/5431 PLL Ref/External Clock Connector

NI Signal Generator

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NI PXI/PCI-5411/5431
PLL Ref/External Clock Connector


The PLL Ref/External Clock connector on the NI 5411/5431 has different uses depending on which NI 5411/5431 you are using.

  • NI PCI-5411

The PLL Ref connector is a phase-locked loop (PLL) input connector that can accept a Reference clock from an external source and phase lock the NI PCI-5411 internal clock to this external clock. The Reference clock should not deviate more than ±100 ppm from its nominal frequency. The minimum amplitude levels of 1 Vpk-pk are required on this clock. You can lock Reference clock frequencies of 1 MHz and 5–20 MHz in 1 MHz steps.

Note  You can phase lock the NI PCI-5411 to other NI devices over the RTSI bus using the 20 MHz RTSI clock signal. You can phase lock the NI PXI-5411 to other NI devices using the 10 MHz backplane clock.

If no external Reference clock is available, the NI 5411 automatically tunes the internal clock to the highest accuracy possible. For more information about PLL operation, refer to Phase Locked Loops and Module Synchronization.

  • NI PCI-5431

You can use the PLL Ref/External Clock connector for phase locking to an external source when the device is not in video mode. The device timing circuit in video mode does not support phase-lock looping. However, if the PLL reference frequency is suitable for video generation, you can generate a video waveform with the device in normal Arbitrary Waveform Generation mode.

  • NI PXI-5411/5431

In addition to phase locking (on the NI 5411), the PLL REF/External Clock connector also provides input from an external Sample clock. You can select this functionality on the NI 5411/5431 through the software. You can feed a TTL/CMOS-level clock to this connector with a maximum frequency of 40 MHz.

Caution  You must not change the external clock while waveform generation is in progress. Only modify the frequency of the external clock before you start the waveform generation or after you stop the waveform generation. NI cannot guarantee the quality of the signal generated, if you change the external clock while waveform generation is in progress.
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