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Master Timebase Synchronization

Last Modified: November 16, 2017

Master Timebase synchronization is the most flexible and powerful synchronization method available on supported devices. It allows you to synchronize all timing for the synchronized devices, even at different rates and regardless of subsystem, in that clocks derived from the Master Timebase start and remain in phase. For counter operations, Master Timebase synchronization ensures the counter timebases remain synchronized without drift, or in phase if the application requires different counter timebase frequencies.

When using Master Timebase synchronization, slave devices replace their onboard oscillator (the Master Timebase) with the Master Timebase from a master device. Each device then derives other clocks from the synchronized oscillators. You must share a Start Trigger for the derived clocks to start in phase.

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Note  

You must start any tasks on slave devices before starting the task on the master device.

You must set two properties on the slave devices to synchronize the Master Timebase. Use the MasterTimebase.Src attribute/property on the slave devices to specify the terminal of the Master Timebase from the master device. Because the slave devices then use an external timebase, you must also use the MasterTimebase.Rate property to specify the rate of the Master Timebase. Instead of hard-coding those values, you can query the Master Timebase rate and source from the master device and set the rate and source on the slave devices to the same values.

Master Timebase synchronization results in skew due to the time required for the clock to travel between devices.

Most devices use a Reference Clock instead of a Master Timebase, thus they use Reference Clock synchronization. Master Timebase synchronization also requires you to share multiple signals and reserve multiple RTSI or PXI trigger lines for those signals. For Sample Clock-timed applications where all devices run at the same rate, you can use Sample Clock synchronization to eliminate the need for a shared Start Trigger, thus the additional RTSI/PXI line. You can also use Sample Clock synchronization to synchronize devices that use a Master Timebase with devices that use a Reference Clock.


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