Black Box Explains...16850 UART..
The 16850 Universal Asynchronous Receiver/Transmitter (UART) features a 128-byte First In First Out (FIFO) buffer. When implemented with the appropriate onboard drivers and receivers, it enables your onboard serial ports to achieve sustained data rates of up to 460.8 kbps.
The 16850 UART includes automatic handshaking (RTS/CTS) and automatic RS-485 line control. It also features external clocking for isochronous applications, a performance enhancement not offered by earlier UARTs.