Siemens SIMATIC ET 200AL System Manual page 918

Connection resources
11.2 Allocation of connection resources
Data record routing also enables transfer of data beyond S7 subnets from an engineering
station connected to PROFINET to various field devices via PROFIBUS.
With data record routing, as with S7 routing, two of the special connection resources for S7
routing are also occupied on every data record router.
Note
Connection resources with data record routing
With data record routing, on the data record router, two special connection resources for S7
routing are occupied. Neither the data record connection nor the allocated connection
resources are displayed in the table 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 29)).
● 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. HMI 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:
A connection resource is occupied in the CPU as long as a session exists between the
OPC UA server of the CPU and an OPC UA client.
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Function Manual, 12/2017, A5E03735815-AF
Communication