Chapter 5
Developing Your Application
NI PXI-4220 User Manual
5-12
ni.com
Synchronization and Triggering
If you have multiple NI PXI-4220 devices, you can synchronize them to
acquire samples at the same time and at the same rate. With SS/H enabled,
and each device synchronized, you can use multiple NI PXI-4220 devices
to acquire and analyze complex signals.
Note
The phase difference is lower between channels on the same device with SS/H than
between channels on different devices.
For multiple NI PXI-4220 devices to start an acquisition simultaneously,
they must all reference a common start trigger. To prevent drift over the
course of the acquisition, they must share a common timebase or sample
clock.
The NI PXI-4220 that generates the start trigger and the timebase for all of
the synchronized devices is called the master. The master NI PXI-4220
exports the shared timing signals through the PXI bus to the slave devices.
Each NI PXI-4220 contains a DAQ-STC chip and is capable of generating
a hardware sample clock based on its timebase clock and start trigger.
When using a shared timebase and start trigger, each slave NI PXI-4220
still generates a hardware sample clock, but it generates the clock using the
timebase and start trigger of the master NI PXI-4220. This causes the slave
device to acquire samples at the same time as the master.
The preferred method of synchronization is to use a shared timebase, but it
is also possible to synchronize multiple NI PXI-4220 devices by sharing
the sample clock between them. This manual only discusses the shared
timebase method.
Synchronizing the NI PXI-4220
Figure 5-3 shows a typical program flow chart for synchronizing the
sample clocks and start triggers of two devices, taking a measurement,
and clearing the data.
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