10 | More about MC6 and AS6?
STOBER
64
05/2018 | ID 442461.04
10.2.2
Synchronization
For spatially distributed processes that require simultaneous actions, the EtherCAT master and
slaves absolutely must work in synchronization with each other in the same cycle. EtherCAT
provides two different methods for synchronizing the master and slaves: a SyncManager event
(SM-Sync) and distributed clocks (DC-Sync). The FreeRun state exists if the master and slaves
are not synchronized.
Each EtherCAT Slave Controller has a SyncManager that manages the memory units of a
slave. The slave controller indicates incoming process using an interrupt signal that is used to
synchronize individual EtherCAT slaves for SM-Sync; an additional interrupt signal is
responsible for synchronization for DC-Sync.
10.2.2.1
SM-Sync: Synchronization using SyncManager event
In the case of adjustment using a SyncManager event, the EtherCAT slaves synchronize using
incoming data as the event.
I O
I O
I O
I
I
I
Master task
Slave task
Output (waiting)
Output (waiting)
T
Master cycle time
T
Master cycle time
Time
T
PLL phase
offset
T
PLL phase
offset
T
Slave cycle time
Fig. 24: SM-Sync – Synchronization using SyncManager event
The following times are significant for SM-Sync.
§
Master cycle time
... Time within which a master task is continuously called up and processed.
§
Slave cycle time
... Time within which a slave task is continuously called up and processed.
§
PLL phase offset
... Time for which the beginning of the individual slave task can be shifted. The task
beginning can only be shifted within the scope of the slave cycle time.
The quality of synchronization using SM-Sync suffers in the case of delays in the PDOs from
master to slave.
Because master jitter immediately has an immediate impact on the slaves, this synchronization
method leads to a poorer result than an adjustment using distributed clocks.