Table 3. PXIe-6674T Signals (Continued)
Signal Name
Direction
Description
PXIe_DSTARB
Out (to
chassis)
The PXIe_DSTARB lines connect the system timing
module to each peripheral slot in a PXI Express chassis,
allowing the system timing module to send out high
speed triggers to every slot. PXIe_DSTARB uses
differential LVDS signaling and is capable of sending out
higher speed trigger signals.
PXIe_DSTARC
In (from
chassis)
The PXIe_DSTARC lines connect each peripheral slot in
a PXI Express chassis to the system timing module,
allowing the system timing module to receive high speed
clock and trigger signals from every slot. PXIe_DSTARC
uses differential LVDS signaling.
Generating and Routing Clocks
The PXIe-6674T can generate two types of clock signals. The first clock is generated using the
onboard clock generation circuitry, and the second is generated with a precise 10 MHz
oscillator. The following sections describe the two types of clock generation and explain the
considerations for choosing either type.
Clock Generation
The PXIe-6674T includes built-in advanced clock generation circuitry for generating clock
signals from below 1 Hz to 1 GHz with very fine frequency resolution. The clock generation
circuitry is based on a direct digital synthesis (DDS with an 800 MHz reference phase locked
to PXIe_CLK100. This allows the DDS to generate a 150 MHz to 300 MHz signal with
microhertz resolution. The output from the DDS can then be divided down to lower
frequencies, used directly, or multiplied up using a phase locked voltage controlled oscillator.
The individual components which make up the clock generation circuitry are controlled by NI-
Sync software, which allows the user to simply specify the frequency they wish the clock
generation circuitry to produce. NI-Sync will then configure the clock generation circuitry to
give the closest possible frequency match to the requested frequency and do so with the
configuration that gives the lower possible phase noise. The user may request a clock
frequency of 1 GHz (frequencies beyond 1 GHz are possible, but performance is not
specified). The precision of the frequency generated is that of the DDS scaled up or down for
any division or multiplacation done to generate the requested frequency, as shown in
on page 15:
14
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PXIe-6674T User Manual
