Siemens SINAMICS S120 Function Manual page 528

Communication PROFIBUS DP/PROFINET IO
10.3 Communication via PROFINET IO
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, i.e.
mixed operation of RT classes IRT and IRT* is not permissible. Different synchronization
domains can communicate with one another via RT.
With IRT* and IRT, all IO devices and IO controllers must be synchronized with a common
synchronization master.
IRT* drive units can be replaced with IRT drive units in HW Config. The conversion from
IRT* to IRT and vice versa is not performed automatically, but must be made manually.
The HW Config consistency check ascertains whether modules communicating with one
another within a single synchronization domain are all configured to use the same RT
classes: All modules use either IRT* or IRT.
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*: SIMOTION 1 with SINAMICS
● Synchronization domain IRT : SIMOTION 2 with SINAMICS
● SINAMICS, which is assigned to the IO system of SIMOTION 1, is arranged in the
Figure 10-45 RT communication across the limits of synchronization domains
- - - communication outside synchronization domains
Update cycles and send cycles for RT classes
Definition of update cycle/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 it has transferred new data
(inputs) to the IO controller within the update cycle. The send cycle is the shortest possible
update cycle.
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topology in such a way that its RT communication must be conducted through the IRT
synchronization domain.
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions