Text Input field formatting

Hi experts,

I have to customize an old VC app (NW 7.0).

The requirement is quite simple :

I have a text input field which can get input from a user via 2 differents ways

• the user enters a 13 char product code
• the user uses a barcode scanner which prints a string where there is the 13 char product code (amongst other info, the string is longer).

So to handle both cases I wrote this formatting formula but it's not working when I try to use the barcode scanner :

IF(!ISNULL(@I_EAN13)&LEN(@I_EAN13)>13,MID(@I_EAN13,4,LEN(@I_EAN13)),@I_EAN13)

The input field remains the same with all the data I don't need from the barcode.

How can I update the input field value if I'm in the barcode scanner case ?

Regards