SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
The bootloader provides a method to automatically detect the UART baud rate being used to communicate with it. To synchronize with the host, the bootloader must receive 2 bytes with the value of 0x55. If the synchronization succeeds, the bootloader returns an ACK consisting of 2 bytes with the values of 0x00 and 0xCC.
If synchronization fails, the bootloader waits for the next synchronization attempt. In the automatic detection function, the UART0 RX pin is monitored for edges using GPIO interrupts. When enough edges are detected, the bootloader determines the ratio of baud rate and frequency needed to program the UART.
The UART module system clock must be at least 16 times the baud rate; thus the maximum theoretical baud rate is 3 Mbaud (48 MHz divided by 16), but is limited to 1.2 Mbaud by the firmware that performs the detection of the host transfer rate.