Instructions:
Proceed as follows to make a screen selection by entering a screen number.
In this example the relevant screen is selected via a text list. 
At the end of this entry there is a free download of a sample program.
 

No.	Procedure
1	Creating tags: Create a tag in your WinCC flexible project, e.g. "Screen_Selection_1" tag. It is not absolutely necessary to have a connection to the controller. In the tag properties "Events > Change value", select the system function "ActivateScreenByNumber" (System functions > Screens). Insert the "Screen_Selection_1" tag in the "Screen number" parameter. Fig. 01
2	Creating a text list: In order to select the individual pictures, create a text list containing the names of all the pictures. Enter the number of each picture in the "Value" field beside the corresponding name of the picture. Fig. 02
3	Symbolic IO field: Configure a symbolic IO field in the permanent window, for example. Insert the "Screen_Selection_1" tag in the "Process" tag field. Fig. 03
4	Function description: Select a screen through the symbolic IO field. If there is a change of values in the "Select_Screen_1" tag, the function "ActivateScreenWithNumber" is executed. Depending on the default in the tags, the screen changes to the screen configured.

The attached download contains the archived STEP 7 project and integrated WinCC flexible project, along with the functions described above.

 Attachment1:  Project_1.zip ( 2434 KB )

Runnability and test environment:
The example can be used on all the CPU types of SIMATIC S7-300, S7-400 and WinAC.
The following table lists the components that have been used to create this entry and verify the functions described.
 

Components	Product and version designation
PC operating system	Microsoft Windows XP SP2
Standard tools	STEP 7 V5.3 SP3
Engineering tools	-
HMI software	WinCC flexible 2005 SP1
HMI devices	MP 370 Touch
Controllers	S7 CPU 315-2DP

Table 1: Creation environment of the download attached