Description:
Every communication connection needs connection resources on the respective device:

• for the PG-communication
• for the OP-communication
• for the S7-basis communication

1. C7-CPU
In principle several connections can be managed by the C7 CPU. These are split up as follows:

• A connection is reserved for the PG. It can't be used for other purposes. Consequently it is guaranteed at any time, that a (service-) PG can be connected in case of an error.
• A second connection is reserved for the C7-OP. 
• Furthermore "spare" connections are available for user-defined use (view table 1).

Hint:
The communication modes "Global data" (GD) and "Decentralized periphery" (DP) do not use the connection resources.

2. C7-OP
A C7-OP can manage several connection resources. These are split up as follows:

• A connection of the C7-OP is reserved for the ("internal") C7 CPU (exception C7 613).
• Further connections are at the users disposal, which can be assigned to user-defined "external" controllers. This might be further C7, S7 300 or S7 400 controllers.

Assign the connection resources in the configuration environment of ProTool or ProTool/Lite.
 

C7 device	Number of CPU connections	Number of OP connections
C7-613	8	--
C7-635	12	4
C7-636	16	6

Table 1: Maximum possible communication connections on a C7 device 

A CP 342-5 can be used in order to increase the number communication stations (connections) in the C7-CPU.

More information on this topic area is available in

• the manual on "Communication with SIMATIC" in Entry ID 1254686.
• the manual on "SIMATIC Complete Device C7-613" in Entry ID 13125532.
• the manual on "SIMATIC Complete Device C7-635" in Entry ID 11559312.
• the manual on "SIMATIC Complete Device C7-636" in Entry ID 18230904