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Chapter 3
Hardware Overview
The remainder of this chapter describes how these signals are used, acquired, and generated by
the NI PXI-6683 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-6683 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-6683 Series is
also capable of generating arbitrary digital events, to be used as triggers.
TCXO, PXI_CLK10, and Clock Disciplining
The NI PXI-6683 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 and adjust the oscillator's
control voltage to compensate for temperature variations according to the crystal's known
frequency variation across its operating temperature range.
An NI PXI-6683 module in the system timing slot 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.
PFI<0..2>
In/Out
The Programmable Function Interface pins on the
NI PXI-6683 Series route timing and triggering
signals between multiple PXI chassis. A wide
variety of input and output signals can be routed
to or from the PFI lines.
PFI<0> also can function as an input for IRIG-B
DC or AM.
PXI_TRIG<0..7>
In/Out
The PXI trigger bus consists of eight digital lines
shared among all slots in the PXI chassis. The
NI PXI-6683 Series can route a wide variety of
signals to and from these lines.
Table 3-5.
NI PXI-6683 Series I/O Terminals (Continued)
Signal Name
Direction
Description