You're right, I can use Function keys to modify I/O field values in Output mode, but there's a problem. This HMI (KTP400 Color) screen contains several I/O fields. In Input/Output or Input mode, the operator can select one of them by tapping the screen, but then the on-screen keyboard pops up. In Output mode though, there's no way for the operator to select which I/O field to modify because in Output mode they can't receive focus by tapping the touch screen.
What I would like is for the operator to be able to select one of several I/O fields by tapping it, and then not have the on-screen keyboard pop up -- instead modify the field value up/down using a couple of Function keys. Is this possible?