Siemens Simatic S7-200 System Manual page 77

Programming with Symbolic Addresses
Before you start entering your program, make sure the ladder view is set for symbolic
addressing. Use the menu command View
mark next to the menu item, which indicates that symbolic addressing is enabled.
Note
Symbol names are case-sensitive. The name you enter must match exactly the uppercase
and lowercase characters entered in the symbol table. If there is any mismatch, the cursor
stays on the element and the message "Invalid parameter" appears in the status bar at the
bottom of the main window.
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
Getting Started with a Sample Program
Symbolic Addressing and look for a check
4-9