Connection multiplexing means that all S7 connections that arrive at the CP are switched to one connection, which then leads finally to the CPU. This means that the CP always reserves one connection resource in the CPU. Here it doesn't matter whether or not an S7 connection has already been configured. All other bilateral S7 connections that you configure reserve no other connection resource in the CPU. Another characteristic is that the communication performance diminishes with every connection configured. The advantage is that with multiplexing you can configure more connections than without.
In Fig. 01 you see that a total of seven S7 connection have been configured, but only two connection resources are reserved in the CPU.
The following table shows which SIMATIC S7-300 Ethernet CPs support connection multiplexing.
Proceed as follows to activate connection multiplexing in your CP.
||Open your CP's Properties in the Hardware Configuration.|
||Switch to the "Options" tab.|
||Check the option "Reserve CPU connection resource".
||Save and load the settings into your controller.|
Please note the following points:
- Connection multiplexing only works for fully specified bilateral S7 connections.
- As soon as connection multiplexing is activated, a CPU connection resource is reserved, even if a connection has not yet been configured.
- A separate connection resource is reserved in the CPU for each unilateral S7 connection.
- Only the fully specified unilateral S7 connections are displayed in the CPU's Properties dialog ("Communication" tab). The multiplex connection and the unspecified connections are not displayed, but still count. When communication services log on (the connection is set up), the CPU connection resources are reserved in chronological order.
You have a CPU that can handle a maximum of 6 connections. Take away the connections for PG/OP Communication, that leaves 4 connections for the S7 communication (value for S7 Standard Communication has been set to 0).
You configure one or more bilateral S7 connections to other devices. These connections run via the multiplexing, i.e. only one resource is reserved in the CPU. But this is not displayed in the Properties.
Now you want to set up 4 connections to the CPU from another device (e.g. OPC server). Each of the connections is configured unilaterally and therefore each requires a separate connection resource in the CPU. Now in the CPU Properties you see that 4 connections are configured. And you cannot create any more connections. It is furthermore possible to create a few more unspecified connections, which are likewise not displayed. Nor do you get any warning from NetPro.
If you test the connections via the OPC Scout, for example, you find that one of the four connections cannot be set up by the OPC server.
The reason for this is that one connection resource is already reserved by the multiplexing and so only 3 other S7 connections are possible.