Chapter 10 Digital Routing and Clock Generation
© National Instruments Corporation 10-3 NI 6238/6239 User Manual

10 MHz Reference Clock

The 10 MHz reference clock can be used to synchronize other devices to
your M Series device. The 10MHz reference clock can be routed to the
RTSI<0..7> terminals. Other devices connected to the RTSI bus can use
this signal as a clock input.
The 10 MHz reference clock is generated by dividing down the onboard
oscillator.
Synchronizing Multiple Devices
With the RTSI bus and the routing capabilities of MSeries devices, there
are several ways to synchronize multiple devices depending on your
application.
To synchronize multiple devices to a common timebase, choose one
device—the initiator—to generate the timebase. The initiator device routes
its 10 MHz reference clock to one of the RTSI<0..7> signals.
All devices (including the initiator device) receive the 10MHz Reference
Clock from RTSI. This signal becomes the external reference clock. A PLL
on each device generates the internal timebases synchronous to the external
reference clock.
On PXI systems, you also can synchronize devices to PXI_CLK10. In this
application the PXI chassis acts as the initiator. Each PXI module routes
PXI_CLK10 to its external reference clock.
Another option in PXI systems is to use PXI_STAR. The Star Trigger
controller device acts as the initiator and drives PXI_STAR with a clock
signal. Each target device routes PXI_STAR to its external reference clock.
When all of the devices are using or referencing a common timebase, you
can synchronize operations across them by sending a common start trigger
out across the RTSI bus and setting their sample clock rates to the same
value.
Real-Time System Integration Bus (RTSI)
Real-Time System Integration (RTSI) is set of bused signals among devices
that allow you to do the following.
• Use a common clock (or timebase) to drive the timing engine on
multiple devices