31.3.1.2 BREAK Character

The BREAK character is used to reset the internal state of the UPDI to the default setting. This is useful if the UPDI enters an Error state due to a communication error or when the synchronization between the debugger and the UPDI is lost.

To ensure that a BREAK is successfully received by the UPDI in all cases, the debugger must send two consecutive BREAK characters. The first BREAK will be detected if the UPDI is in Idle state and will not be detected if it is sent while the UPDI is receiving or transmitting (at a very low baud rate). However, this will cause a frame error for the reception (RX) or a contention error for the transmission (TX), and abort the ongoing operation. The UPDI will then detect the next BREAK successfully.

Upon receiving a BREAK, the UPDI oscillator setting in the ASI Control A (UPDI.ASI_CTRLA) register is reset to the 4 MHz default UPDI clock selection. This changes the baud rate range of the UPDI, according to Table 31-1.