Siemens SIMATIC S7-1500 System Manual page 148

Setting the clock system
You have configured the technology I/Os as isochronous. Next, set the clock system.
Make the following settings in accordance with whether you are operating the X142
technology I/Os in independent or coupled isochronous mode:
● For independent isochronous mode or if the X142 technology I/Os are the leading clock
system
– Set the required cycle time.
– Assign the "MC Servo" OB the clock system of the technology I/Os.
Note
You cannot operate the X142 technology I/Os in isochronous mode separately from
SINAMICS Integrated. If you want to operate X142 technology I/Os and SINAMICS
Integrated in isochronous mode simultaneously, always set coupled isochronous mode.
● For coupled isochronous mode:
– Assign the leading clock system to the clock system of the technology I/Os.
SIMATIC Drive Controller
System Manual, 11/2019, A5E46600094-AA
You can find details of how to assign the leading clock system in Setting the clock
system (Page 150).
Configuring
7.11 Configuring the clock system
147