XR21B1421 USB HID to UART Bridge MaxLinear XR21B1421 Enhanced 1-Ch Full-Speed USB HID to UART Bridge is an enhanced Universal Asynchronous Receiver and Transmitter (UART) bridge to HID class USB interface. The USB interface is USB 2.0 (Full-Speed) compliant, with a 12Mbps USB data transfer rate. The XR21B1421 also supports USB suspend, resume and remote wakeup operations.