Siemens SIMATIC PROFINET Function Manual page 164

Functions
5.5 Real-time communication
5. In the Inspector window, navigate to "Advanced options > Real time settings >
Synchronization".
Figure 5-47 IRT configuring sync slave
6. Activate the RT class "IRT". The IO device will then automatically be assigned the
synchronization role "sync slave".
7. You can check and correct your settings at any time using the "Domain settings" button.
Or
1. Highlight the PROFINET IO system in the network view.
2. Click on the PROFINET IO system.
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PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG