BC1.2 detection 需經過下圖的五個步驟
Charging ports exist: charging downstream ports (CDP), supporting data transfers as well,
Dedicated charging ports (DCP), without data support.
Accessory charging adapters (ACA) are introduced. By using an accessory charging adapter, a device providing a single USB port can be attached to both a charger, and another USB device at the same time.
Battery charging specification Revision 1.2