Siemens SIMATIC PROFINET Function Manual page 105

The next figure shows the data exchange between the higher- and lower-level IO system.
The individual communication relations are explained below based on the numbers.
Figure 5-11
①
Data exchange between higher-level IO controller and normal IO-device
In this way, the IO controller and IO devices exchange data through PROFINET.
PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG
Data exchange between higher- and lower-level IO system
5.2 Intelligent IO devices (I-devices)
Functions
105