Siemens SIMATIC S7-1500 System Manual page 216

Configuring
9.11 Configuring the clock system
X142 technology I/Os clock system
Proceed as follows to set the clock system of the X142 technology I/Os:
1. In the device view of STEP 7, select the CPU of the SIMATIC Drive Controller.
2. Navigate to "Advanced configuration" > "Isochronous mode" in the properties of the CPU.
3. Select the required settings from the "Source of send clock" drop-down list in the
"Isochronous mode for local modules" section.
Figure 9-42 Technology I/O clock system
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SIMATIC Drive Controller
System Manual, 11/2023, A5E46600094-AD