Document MT0605P.E
© Xsens Technologies B.V.
MTi User Manual
57
5.5 Triggering and synchronization
In case multiple systems are used during a measurement it is important to have the measurement
data synchronized between the systems. Processing synchronised data is much easier because there
is no need to resample the data to compensate for timing inaccuracies like clock drift and clock
deviations. Synchronization using multiple systems involves 2 important issues: starting the
measurement at the same time and having a fixed time relationship of the sampling instances. This
section will explain how the MTi must be setup when using multiple measurement systems.
All MTi’s have a minimum of 3 GPIOs, offering the MTi capabilities to be triggered by external devices,
trigger external devices or synchronize clock drift. These three user scenarios are explained in the
following subsections.
5.5.1
External device triggers MTi (Send Latest)
In the following figure, a possible configuration is shown where a Motion Tracker and Device A are
synchronised. In this example, a clock generator triggers device A and an MTi ensuring that the two
devices are synchronized with each other.
The output of the clock generator can be directly connected to the MTi.
NOTE:
Always check if the SyncIn specification matches with the trigger signal.
Once a SyncIn signal or a
ReqData
message is received, the MTi will output the latest available data.
It is possible to delay the data to be sent, to choose whether the SyncIn signal needs to be triggered
on rising edge or falling edge etc. The internal clock determines when data is available. This data is
transmitted only if a trigger is detected on the SyncIn line or when polled (
ReqData
). This means that
the trigger instance will not coincide with the availability of the data. Because two different clocks are
used the time difference between the trigger instance and the last sampling instance may vary during
the measurement and at most with a time equal to the used sampling period.
5.5.2
Marker in MT data (Trigger Indication)
Next to let the MTi send data to the computer, it is also possible to incorporate a trigger indication in
the MTData2 packet (Status Word). The data will not be affected by the trigger indication; the data is
marked with the pulse received.