If the USART is programmed to operate in Asynchronous mode, the selected clock is first divided by the value of US_BRGR.CD. The resulting clock is provided to the receiver as a sampling clock and then divided by 16 or 8, depending on the value of US_MR.OVER.
If OVER is set to ‘1’, the receiver sampling is eight times higher than the baud rate clock. If OVER is set to ‘0’, the sampling is performed at 16 times the baud rate clock.
The baud rate is calculated as per the following formula:
This gives a maximum baud rate of peripheral clock divided by 8, assuming that the peripheral clock is the highest possible clock and that the OVER is written to ‘1’.