StarTech.com 6ft (1.8m) 1-Port Professional RS422/485 USB Serial Cable Adapter with COM Retention,

Add an RS422/485 serial port to your system through USB; features COM port retention

The ICUSB422 6ft Professional RS422/485 USB Serial Cable Adapter with COM Port Retention lets you connect RS422 or RS485 serial devices to your USB-enabled computer. The adapter features a 9-pin (DB9) male serial connector as well as dipswitch controls for easy port configuration, and requires minimal software.

The serial adapter is USB-powered, eliminating the aggravation of requiring an external power adapter. With COM port retention, assigned port settings are saved, so you can disconnect and reconnect the adapter with virtually no configuration required on the host computer.