[Koha] Make a subfield required

Hi guys, we are implementing koha and i have an issue. I want to make the subfield "p" of the field 952 when I add an item to be required. I have it on autocomplete, but to actually autocomplete it I have to click the textbox so the event will be launch, I want to avoid that the user can insert an item without a barcode. Thx! Sergio Scotto __________ Informacion de ESET Endpoint Antivirus, version de la base de firmas de virus 12007 (20150728) __________ ESET Endpoint Antivirus ha comprobado este mensaje. http://www.eset.com