All recent (not high-availability) S7/M7 300/400s (incl. WinAC Slot 41x) and C7-600 CPUs have simple functions (SFCs) for transferring small volumes of data via S7 connections. The connections are not configured, but are set up explicitly when the SFC is called and transfer the data either via the MPI bus or via PROFIBUS DP.
Like S7 communication, S7 basic communication also uses the S7 protocol for data transfer. The S7 protocol is on Layer 7 (Application Layer) of the ISO-OSI reference model, because the system interface used is purely for application data.
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Fig. 01: ISO-OSI reference model
|Type of service
|I_PUT / I_GET
||Permits reading / writing of data of an I slave on the PROFIBUS DP.|
|X_PUT / X_GET
||Permits reading / writing of data of another MPI or backplane bus node.|
- A detailed description of the I and X functions is available in the sample application "Communication with SIMATIC S7", section 3.1.2 in Entry ID: 20982954.
- An example of "Client / Server Communication with (I) Slaves via S7 Basic Communication (I_PUT/ I_GET)" is available in Entry ID: 20987910.
Not configured connection, X_SEND, X_RCV