The 'DP' command, or 'DEPT.' button, is used to ring up items which haven't been properly entered into the system.
To use this key you will need to know the 'taxonomy id' of the department/category you want to ring the item up into. Instructions on how to do this will be added soon.
For example, if an item doesn't have a sku, costs $5.00 and is part of the Toys category (which a taxonomy ID of, say, 22) you would enter '500DP22' or click 5, 0, 0, DEPT., 2, 2, ENTER.