Double Speed Operation

Double speed operation allows for higher baud rates under asynchronous operation with lower peripheral clock frequencies. This operation mode is enabled by writing the RXMODE bit in the Control B register (USART.CTRLB) to CLK2X.

When enabled, the baud rate for a given asynchronous baud rate setting shown in Table 1 will be doubled. In this mode, the receiver will use half the number of samples (reduced from 16 to 8) for data sampling and clock recovery. This requires a more accurate baud rate setting and peripheral clock. See Asynchronous Data Reception for more details.