In dual clutch transmissions two gears may be engaged at the same time in order to reduce shift time to sole clutch transition instead of full selection procedure. Properly setup preselection greatly reduces input lag.
Preselection is based on tables, but can also be forced. Two individual inputs can be assigned as either force UP or DOWN shift preselection. High (YES) state of input forces preselection into desired direction, for example brake pressure input would usually be assigned as force DOWNshift preselection – while not pressed properly calibrated input reports NO and pressed would report YES. State YES forces then preselection as downshift preselection (usually in braking scenario).
If both force inputs report YES then preselection will be NONE – transmission won’t have preselected another gear and second branch would stay in NEUTRAL.
Hint #1: No preselection is way better than bad preselection 🙂