Chapter 9 Digital Routing and Clock Generation© National Instruments Corporation 9-3 M Series User Manual10 MHz Reference ClockThe 10 MHz reference clock can be used to synchronize other devices toyour M Series device. The 10 MHz reference clock can be routed to theRTSI <0..7> terminals. Other devices connected to the RTSI bus can usethis signal as a clock input.The 10 MHz reference clock is generated by dividing down the onboardoscillator.Synchronizing Multiple DevicesWith the RTSI bus and the routing capabilities of M Series devices, thereare several ways to synchronize multiple devices depending on yourapplication.Note RTSI is not supported on USB devices.To synchronize multiple devices to a common timebase, choose onedevice—the initiator—to generate the timebase. The initiator device routesits 10 MHz reference clock to one of the RTSI <0..7> signals.All devices (including the initiator device) receive the 10 MHz referenceclock from RTSI. This signal becomes the external reference clock. A PLLon each device generates the internal timebases synchronous to the externalreference clock.On PXI systems, you also can synchronize devices to PXI_CLK10. In thisapplication the PXI chassis acts as the initiator. Each PXI module routesPXI_CLK10 to its external reference clock.Another option in PXI systems is to use PXI_STAR. The Star Triggercontroller device acts as the initiator and drives PXI_STAR with a clocksignal. Each target device routes PXI_STAR to its external reference clock.Once all of the devices are using or referencing a common timebase, youcan synchronize operations across them by sending a common start triggerout across the RTSI bus and setting their sample clock rates to the samevalue.
