Here is a app note from Microchip describing how to implement the Auto-Baud detection for UART operation on dsPIC30 digital signal processors. This function is useful when the oscillator of the dsPIC is unknown and/or the baud rate is unknown.
All current dsPIC30F devices have a UART peripheral with Auto Baud capability. The signal on the UART receive pin (RX pin) can be internally routed to an Input Capture module to time the edges of the incoming signal. From that timing the software can set up the UART at the correct baud rate. Auto Baud is useful when the baud rate of the incoming data is unknown and when the oscillator frequency of the processor is unknown. RC oscillators are often inaccurate and drift over time so systems with RC oscillators are ideal candidates for using Auto Baud.