Please check the following points in your project.
 

No.	Procedure
1	S7DOS must be installed. S7DOS is installed automatically in WinCC version V5.0 + SP2 and higher. If necessary, you can install it from the WinCC CD. Start WinCC Setup and in the "Select Components" dialog you choose "Communication > S7DOS" Fig. 01
2	The access point defined in the PG/PC interface must match the logical device name of the MPI channel. For example, to use the "S7ONLINE" access point, you must set the PG/PC interface on your MPI communications processor. In the Control Panel you open the "Set PG/PC Interface" program. Select "S7ONLINE" as Access Point and then select your MPI communications processor. If it is not shown in the window, you can install it using the "Select..." button. Fig. 02
3	A communication channel must exist. Open your WinCC project and add your channel to the Tag Management. To do this, right-click to open the "Add new driver" dialog box and install the "SIMATIC S7 Protocol Suite.CHN" WinCC communications driver. Fig. 03
4	The access point must be correct. Set the logical device name of the MPI channel to the "S7ONLINE" access point that you selected under (2). In Tag Management you double-click on the communications driver "SIMATIC S7 PROTOCOL SUITE". Right-click on the "MPI" channel and click on the menu command "System Parameter". Click on the "Unit" tab and select the item "S7ONLINE" item in the drop-down list for "Logical device name". Fig. 04
5	You must create a connection. Then right-click to add a new connection to your S7 or S7 program and give it a name. Example: "S7Programm_AS1". Fig. 05
6	The connection properties must be correct. In the dialog that opens (in point 5) you click on the "Properties" button and set the connection parameters there. In this case, the CPU has the MPI address "30" and the MPI segment has the ID "0". The CPU is slotted in rack number 0, slot 3. Fig. 06

Keywords:
Connection, Communication settings, MPI interface