Communications services
3.3 Overview of connection resources
Communication
Function Manual, 11/2019, A5E03735815-AH
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3.3 Overview of connection resources
Connection resources
Some communications services require connections. Connections allocate resources on the
CPUs, CPs and CMs involved (for example memory areas in the CPU operating system). In
most cases one resource per CPU/CP/CM is allocated for a connection. In HMI
communication, up to 3 connection resources are required per HMI connection.
The connection resources available depend on the CPU being used, the CPs and CMs and
must not exceed a defined high limit for the automation system.
Available connection resources in a station
The maximum number of resources of a station is determined by the CPU.
Each CPU has reserved connection resources for PG, HMI and web server communication.
In addition, there are available resources for other communication services, e.g. for SNMP,
e-mail connections, HMI and S7 communication as well as for open communication.
When are connection resources allocated?
The time for allocation of connection resources depends on how the connection is set up,
automatic, programmed or configured (see section Setting up a connection (Page 27)).
Additional information
You will find more detailed information on the allocation of connection resources and the
display of connection resources in STEP 7 in the section Connection resources (Page 307).
3.4 Setting up a connection
Automatic connection
STEP 7 sets up a connection automatically (for example PG or HMI connection) if you have
connected the PG/PC interface to an interface of the CPU physically and have made the
interface assignment in STEP 7 in the "Go online" dialog.
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