Siemens SIMATIC PROFINET Function Manual page 163

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 5-46 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.
PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG
Functions
5.5 Real-time communication
163