Hello Aleksandr;

In the Step 7 v5.x instruction libraries, you can see the IEC standard functions. These include 2 blocks that should interest you, FC 37 (Str to DI) and FC 38 (Str to I). You can find descriptions of these blocks in this article:

https://support.industry.siemens.com/cs/ww/en/view/10913338

If you plan to use these functions you must first turn your char variables into  string, as defined in Siemens Step 7. A string' first 2 bytes contain specific information for the compiler, the maximun length of the string and the actual length used. Then the first, second, ... character.

So  Str[4] actually occupies 6 bytes, of which 4 are the actual string char values.

Look at this discussion for hints on converting an array of chars to a string in Step 7.

https://support.industry.siemens.com/tf//ww/en/posts/converting-the-types/213753/?page=0&pageSize=10

Hope this helps, 

Daniel Chartier