Automatic baud rate detection (ABR, autobaud) refers to the process by which a receiving device (such as a modem) determines the speed, code level, start bit, and stop bits of incoming data by examining the first character, usually a preselected sign-on character (syncword) on a UART connection.
These type of baud rate detection mechanism are supported by many hardware chips including processors such as STM32[1] MPC8280, MPC8360, and so on.
Many protocols begin each frame with a preamble of alternating 1 and 0 bits that can be used for automatic baud rate detection.
FlexWire receivers use the sync byte to precisely set their UART bit-clock frequency without a high-precision oscillator.
Before receiving any input data, most modems use a default baud rate of 9600 for output.