Master Synchronization Telegram
The SERCOS interface master begins a communication
cycle by transmitting a Master Synchronization Telegram
(MST), which sets the timing and synchronization for
the network. Each slave device (drive or I/O) synchronizes
its clock from the MST, then uses this timing to calculate
when to acquire feedback signals and other processing.
The MST data field also contains information. Upon
startup, the SERCOS interface loops go through an
extensive initialization procedure, where drives are
assigned an operating mode (speed, torque or position),
and the exact configuration of their cyclic data.
They're also told to synchronize and phase lock their
internal loop-closure frequency, eliminating the risk
of harmonics. Cyclic communication doesn't begin until
this initialization is complete. The MST data field
indicates whether the loop is in one of the initialization
phases or in the communication cycle.
Master Synchronization Telegram
Structure
Master Synchronization Telegrams last only 30 µsec,
but they are extremely important because they set
the timing and synchronization for the entire loop.
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