Description
When you configure input and output modules, it is possible to create symbols for the IO addresses. However, you should not change symbols or their addresses afterwards in the hardware configuration. If you do so, channel driver blocks that are already connected in the CFC chart might receive unwanted addresses. Always use the symbol table to change symbols that are already created. You can edit the symbol table directly or use the export/import function with a spreadsheet.

Below we describe what you should watch out for when changing addresses of symbolic addresses already connected in the CFC chart.

Instructions
The symbols below were configured for inputs on different modules during hardware configuration.
 

Symbol	Address	Module
Input 1	IW 512	Analog Input Module AI 8x13Bit, address range: 512..527
Input 2	IW 528	Analog Input Module AI 8x13Bit, address range: 528..543

The two inputs have already been connected to the associated driver blocks in the CFC chart. The PLC program was compiled with the "Create module driver" option.

Fig. 01: Channel driver blocks in the CFC chart

Following subsequent changes to the wiring, it is now necessary to change the addresses of the symbols. If you were to make changes in the hardware configuration, this would lead to an unwanted interconnection in the PLC program.
Proceed as follows to ensure that the driver blocks are interconnected to the correct hardware addresses.
 

No.	Procedure
1	Open the symbol table of the S7 program and search for the symbols of the inputs. Fig. 02: Symbols of the module inputs
2	Change the values in the Address column. After you have changed the first value, the system recognizes that two identical addresses are present and marks this as a conflict. After you have changed the second address, save the symbol table. Fig. 03: Changing addresses Also in the symbol editor of the hardware configuration the symbols are correctly displayed now. Fig. 04: Changed symbols in the editor of HW-Config Note The connection of the driver block is connected with the new address only if you change the address in the symbol table. The addresses for monitoring the module (MS, Mode, DataXchg) are then also changed. However, if you change the name in the "Symbol" column, only the symbolic name changes. The address and the connection to the module drivers remain unchanged.
3	Recompile the PLC program with the "Create module driver" option and update the view (F5) in the CFC chart. With this procedure you have changed the address of the process value connection and the interconnection of the connections (MS, Mode, DataXchg) to the module drivers. Fig. 05: New interconnection of the channel driver blocks

Creation environment
The pictures in this FAQ were created with SIMATIC PCS 7 V7.1 SP3.