Siemens SIMATIC S7-400H System Manual page 230

Communication
14.1 Communication services
Options for closing the communication connection
The following events cause the communication connection to be closed:
● Program cancellation of the communication connection with FB 66 "TDISCON".
● The CPU state changes from RUN to STOP.
● At POWER OFF / POWER ON
Connection diagnostics
In Step7, you can read detailed information on the configured connections by selecting
"Module state -> Communication -> Open communication over Industrial Ethernet".
Reference
For detailed information on the blocks described above, refer to the
230
STEP 7 Online Help.
System Manual, 03/2012, A5E00267695-11
S7-400H