Siemens SINUMERIK 840D sl Configuration Manual page 85

You can obtain these values automatically from the "NCK" isochronous OB or set them
manually.
Note
Restriction on the use of NCU Link
The combination of isochronous PROFINET NC peripherals (drives, inputs/outputs) and
NCU-Link is not supported.
SINUMERIK STEP 7 Toolbox V14 SP1
Configuration Manual, 05/2017, A5E41846325
Configuring networks
4.5 Configuring PROFINET IO with IRT
85