Chapter 3
Using the NI PXI-4204
©
National Instruments Corporation
3-19
Synchronization and Triggering
If you have multiple NI PXI-4204 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-4204 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-4204 devices to start an acquisition simultaneously,
they all must 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-4204 that generates the start trigger and the timebase for all of
the synchronized devices is called the master. The master NI PXI-4204
exports the shared timing signals through the PXI bus to the slave devices.
Each NI PXI-4204 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-4204
still generates a hardware sample clock, but it generates the clock using the
timebase and start trigger of the master NI PXI-4204. 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-4204 devices by sharing
the sample clock between them. This manual only discusses the shared
timebase method.
Synchronizing the NI PXI-4204
Figure 3-7 shows a typical program flow chart for synchronizing the
sample clocks and start triggers of two devices, taking a measurement,
and clearing the data.
