Chapter 3
Hardware Overview
NI PXI-6682 Series User Manual
3-8
ni.com
The remainder of this chapter describes how these signals are used,
acquired, and generated by the NI PXI-6682 Series hardware, and explains
how you can use the signals between various locations to synchronize
events in your system.
Clock and Event Generation
The NI PXI-6682 Series can generate two types of clock signals. The first
type is generated with a precise 10 MHz oscillator, and the second is
generated with the synchronized timebase. The following sections describe
the two types of clock generation and explain the considerations for
choosing either type. In addition to time-synchronized clock signals, the
NI PXI-6682 Series is also capable of generating arbitrary digital events, to
be used as triggers.
PXI_CLK10 and TCXO
The NI PXI-6682 Series features a precision 10 MHz TCXO. The
frequency accuracy and stability of this clock is greater than the frequency
accuracy and stability of the native 10 MHz PXI backplane clock
(PXI_CLK10).
The main source of error in most frequency reference oscillators is
temperature variation. The TCXO contains circuitry to measure the
temperature of the oscillator. It uses the temperature to adjust its frequency
output according to the crystal’s known frequency variation across its
operating temperature range.
An NI PXI-6682 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 TCXO. All other PXI modules in the
chassis that reference the 10 MHz backplane clock benefit from this
improved reference. The TCXO does not automatically replace the native
10 MHz clock; this feature must be explicitly enabled in software. The
TCXO output also can be routed out to the
CLKOUT
connector.
Note
The 10 MHz TCXO signal is freerunning. It is not disciplined to the board’s time
reference.
