Many external equipment will all use USB interface in the near future

Customer displays (whether segment display or dot matrix display) will all use USB interface to communicate. Some of will support both USB and 9pin RS232 to communicate.
Cash register will use USB2.0 interface to connect PC to communicate (Can export and import data, brush firmware, debug and etc.). All not support RS232 interface to communicate.
Currency Detector will all use USB interface to connect PC to communicate.(Can update firmware, debug and etc.) All not support RS232 interface.
Barcode scanner will all use USB interface.