The configuration of Siemens Step7 (S7) is differentiated into 2 connections they are bilaterally configured and unilaterally configured. In the bilaterally configured S7 connections can be recognized by the fact they receive a connection ID at both endpoints. The remote endpoint of the S7 connection created is entered automatically in the connection table on the partner side.
Unilaterally configured S7 connections are configured on the module that actively sets up the S7 connection. If an S7-300 or S7-400 station actively sets up the S7 connection, then you call communication blocks FB/SFB14 “GET” and FB/SFB15 “PUT” in the CPU’s user program (client).
You can use these for data communication via unilaterally and bilaterally configured S7 connections. You can only use the communication blocks FB/SFB12 “BSEND” and FB/SFB13 “BRCV” and FB/SFB8 “USEND” and FB/SFB9 “URCV” for data communication via bilaterally configured S7 connections.
There is a connection table with all the configured communication connections at In NetPro. Unilaterally configured S7 connections have no entry in the “Partner ID” column of the connection table. This field remains empty in the connection table. No S7 connection is configured on the server and no communication blocks are called. The server is managed independently by the CPU’s operating system and has resource 0×03. No system data is created for this in the connection partner.