I've found in SAP following statement:
Lowercase Letters 2 This setting determines whether the system converts the text value into uppercase letters. If you check this box, the system uses the value exactly as it’s entered. If you leave the box unchecked, the value entered is converted to uppercase letters in the screen template as, for example, a variable (see Chapter 9).
So I thought that it automatically convert data to UPPERCASE and I switched off this option for some IO. However, when I added MasterData via WebDynpro indeed it converted it to uppercase, but when I tried to load data to DSO I have error that I can't do it because of lowercase letters.
Is there any workaround to convert all Data to uppercase?