UARTs (Universal Asynchronous Receiver/Transmitter) interfaces are physical circuits that convert parallel bits from a microcontroller or CPU into serial bits for transmission or convert received serial bits to parallel bits for use by another microcontroller or CPU. UARTs may use RS232, RS422 or RS485 protocols for data transmission and are selected by number of channels, data rate and additional features such as internal oscillators, timer, counter, GPIO and printer ports.