Siemens SIMATIC ET 200AL System Manual page 1763

Functions
5.5 Real-time communication
Procedure
Proceed as follows to enable an existing IO system for the use of IRT:
1. Select the PROFINET interface of the IO controller.
2. In the Inspector window, navigate to "Advanced options > Real time settings >
Synchronization".
Figure 5-51 IRT configuring sync master
3. Assign the IO controller the role of sync master under "Synchronization role".
4. Select the PROFINET interfaces of an associated IO device.
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PROFINET with STEP 7
Function Manual, 05/2021, A5E03444486-AL