Siemens SIMATIC S7-1500 Function Manual page 315

Connection resources
11.2 Allocation of connection resources
When are connection resources occupied?
The time for the occupation of connection resources depends on how the connection is set
up (see section Setting up a connection (Page 27)).
● Programmed setup of a connection:
As soon as an instruction to establish a connection is called in the user program
(TSEND_C/TRCV_C or TCON), a connection resource is occupied.
With suitable parameter assignment of the CONT parameter of the TSEND_C/TRCV_C
instructions or by calling the TDISCON instruction, the connection can be terminated
following data transfer and the connection resource is available again. When the
connection is terminated, the connection resources on the CPU/CP/CM are available
again.
● Configured connections (e.g. S7 connection):
If you have configured a connection in STEP 7, the connection resource is occupied as
soon as the hardware configuration is downloaded to the CPU.
After using a configured connection for data transfer, the connection is not terminated.
The connection resource is permanently occupied. To release the connection resource
again, you need to delete the configured connection in STEP 7 and download the
modified configuration to the CPU.
● PG connection:
As soon as you have connected the PG to a CPU online in STEP 7, connection
resources are occupied.
● Web server:
As long as you have opened the Web server of the CPU in a browser, connection
resources are occupied in the CPU.
● OPC UA server
Each connection to the OPC UA server of the CPU occupies a connection resource in the
station. This connection resource is released immediately when the connection is
terminated.
● OPC UA client
Each connection that the OPC UA client of the CPU has established to an OPC UA
server occupies a connection resource in the station. When an OPC UA connection is
established, the OPC UA client temporarily occupies an additional connection resource.
When an OPC UA connection is terminated, the connection resource is not released
again until after a wait time of approx. 60 seconds in accordance with RFC 793.
314
Function Manual, 11/2019, A5E03735815-AH
Communication