National Instruments NI PXI-665 Series, User Manual

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Chapter 3 Hardware Overview
An NI PXI-6653 or NI PXI-6652 module in Slot 2 of a PXI chassis can replace the native
PXI 10 MHz backplane frequency reference clock (PXI_CLK10) with the more stable and
accurate output of the OCXO or TCXO. All other PXI modules in the chassis that reference the
10 MHz backplane clock benefit from this more accurate frequency reference. Furthermore, the
DDS chip on the NI PXI-6653 or NI PXI-6652 references its output to the backplane clock and
also takes advantage of the superior OCXO or TCXO accuracy. The OCXO or TCXO does not
automatically replace the native 10 MHz clock; this feature must be explicitly enabled in
software. The OCXO or TCXO output also can be routed out to the
CLKOUT connector.
In addition to replacing the native backplane clock directly, the OCXO or TCXO can phase lock
to an external frequency source. This operation is discussed in detail in the
Using the
PXI_CLK10 PLL
section.
Routing Signals
The NI PXI-665
x
has versatile trigger routing capabilities. It can route signals to and from the
front panel, the PXI star triggers, and the PXI/RTSI triggers.
The NI PXI-665
x
also can route a 10 MHz clock from CLKIN to the PXI 10 MHz reference
clock, or a clock of a different frequency from CLKIN to any number of PXI_STAR lines. The
NI PXI-6653 and NI PXI-6652 can lock the OCXO or TCXO to an external reference clock and
send that to the PXI 10 MHz reference clock. The NI PXI-6653 and NI PXI-6652 can route the
OCXO, TCXO, DDS, or PXI 10 MHz reference clock to
CLKOUT .