Chapter 2 Device Overview
© National Instruments Corporation 2-9 NI 660x User Manual
Note Transfer rates may vary depending on your computer hardware, operating system
and system activity. This benchmark data was determined on an AMD Athlon XP 1800
computer with 128 MB of PC-2100 DDR RAM running Windows XP and LabVIEW using
one counter of the TIO device. For continuous measurements, the transfer rate is the
maximum sustained rate for 30 seconds on one counter.
High Precision Clock (NI 6608)
The accuracy of your time measurement and pulse generation is determined
by the timing accuracy of your counter clock. The NI 6608 device has an
oven-controlled crystal oscillator (OCXO) that provides a highly stable
10 MHz clock that you can use as a GATE or SOURCE of a counter. You
can also use the OCXO as the PXI backplane clock. Modules phase locked
to the PXI backplane clock will acquire the same clock stability as the
NI 6608. For more information, refer to the KnowledgeBase at
ni.com/support and search using keyword phase lock.
Using the OCXO as the SOURCE Counter
Using the OCXO as the timebase source of the counter, you can route the
10 MHz clock to CtrnSource.
Using the OCXO as the 10 MHz PXI Backplane Clock
Your PXI chassis has a built-in 10 MHz backplane clock that is
independently routed to each peripheral slot. An independent buffer on the
chassis drives the clock signal to each peripheral slot with a skew of less
than 1 ns between slots. You can use this common reference clock signal to
synchronize multiple modules in a measurement or control system.
Use the OCXO 10 MHz clock to drive the PXI backplane clock so the
modules in the other slots can take advantage of the stable timebase.
Note On NI PXI-660x devices, the maximum timebase is phase locked to the PXI
backplane clock.
To use the OCXO 10 MHz clock as the PXI backplane clock, plug the
NI PXI-6608 device into the Star Trigger Controller Slot, Slot 2, or the slot
immediately to the right of the controller of the PXI chassis.
By default, NI-DAQ software drives the 10 MHz clock from the OCXO
onto the PXI star trigger so that it is used as the PXI backplane clock. When
the PXI chassis senses a clock on PXI star trigger in Slot 2, the chassis
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