Siemens Sinamics S120 Function Manual page 643

Synchronization domain
The sum of all devices to be synchronized form a synchronization domain. The whole
domain must be set to a single, specific RT class (real-time class) for synchronization,
Different synchronization domains can communicate with one another via RT.
For IRT, all IO devices and IO controllers must be synchronized with a common
synchronization master.
RT allows an IO controller to communicate with a drive unit outside a synchronization
domain or "through" another synchronization domain. As of version 5.4 SP1, STEP 7
supports multiple synchronization domains on a single Ethernet subnet.
Example:
● Synchronization domain IRT : SIMOTION2 with SINAMICS
● SINAMICS, which is assigned to the IO system of SIMOTION1, is arranged in the
Update cycles and send cycles for RT classes
Definition of update time/send cycle:
If we take a single IO device in the PROFINET IO system as an example, this device has
been supplied with new data (outputs) by the IO controller and has transferred new data
(inputs) to the IO controller within the update time. The send cycle is the shortest possible
update cycle.
All cyclic data are transferred within the send cycle. The actual send cycle that can be set
depends on various factors:
● Bus load
● Type of devices used
● Computing capacity available in the IO controller
● Supported send clocks in the participating PROFINET devices of a synchronization
The table below specifies the reduction ratios which can be set between the send cycle and
the update times for IRT "high performance", IRT "high flexibility", and RT.
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
topology in such a way that its RT communication must be established through the IRT
synchronization domain.
Figure 10-43 RT communication across the limits of synchronization domains
domain A typical send cycle is e.g. 1 ms
10.3 Communication via PROFINET IO
Communication
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