© National Instruments
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3-9
Hardware Features
The NI PXI-6653 and NI PXI-6652 perform two broad functions:
•
Generating clock and trigger signals
•
Routing internally or externally generated signals from one location to another
The NI PXI-6651 is primarily a slave module and can only route externally generated signals.
Table 3-3 outlines the function and direction of the signals discussed in detail in the remainder
of this chapter.
Table 3-3.
Signal Descriptions
Signal Name
Direction
Description
PXI_CLK10_IN
Out
This is a signal that can replace the native 10 MHz
oscillator on the PXI backplane. PXI_CLK10_IN
may originate from the onboard OCXO or TCXO
or from an external source.
PXI_CLK10
In
This signal is the PXI 10 MHz backplane clock. By
default, this signal is the output of the native
10 MHz oscillator in the chassis. An NI PXI-665
x
in Slot 2 can replace this signal with
PXI_CLK10_IN.
OCXO Clock
(NI PXI-6653) or
TCXO Clock
(NI PXI-6652)
Out
This is the output of the 10 MHz OCXO or TCXO.
The OCXO and TCXO are extremely stable and
accurate frequency sources.
CLKIN
In
CLKIN is a signal connected to the SMB input pin
of the same name. CLKIN can be routed directly to
PXI_CLK10_IN, be used as a phase lock reference
for the OCXO or TCXO, or be routed to a
PXI_STAR line.
CLKOUT
(NI PXI-6653 and
NI PXI-6652 only)
Out
CLKOUT is the signal on the SMB output pin of the
same name. Either the OCXO clock, TCXO clock,
DDS clock, or PXI_CLK10 may be routed to this
location.
DDS Clock
(NI PXI-6653 and
NI PXI-6652 only)
Out
This is the output of the NI PXI-6653 or
NI PXI-6652 DDS. The DDS frequency can be
programmed with fine granularity from 1 Hz to
105 MHz. The DDS chip automatically phase-locks
to PXI_CLK10.
