33.3.2.3 UPDI Communication Error Handling

The UPDI contains a comprehensive error detection system that provides information to the debugger when recovering from an error scenario. The error detection consists of detecting physical transmission errors like parity error, contention error, and frame error, to more high-level errors like access time-out error. See the UPDI Error Signature (PESIG) bit field in the Status B (UPDI.STATUSB) register for an overview of the available error signatures.

Whenever the UPDI detects an error, it will immediately enter an internal Error state to avoid unwanted system communication. In the Error state, the UPDI will ignore all incoming data requests, except when a BREAK character is received. The following procedure must always be applied when recovering from an Error condition.
  1. Send a BREAK character. See the 33.3.1.2 BREAK Character section for recommended BREAK character handling.
  2. Send a SYNCH character at the desired baud rate for the next data transfer.
  3. Execute a Load Control Status (LDCS) instruction to read the UPDI Error Signature (PESIG) bit field in the Status B (UPDI.STATUSB) register and get the information about the occurred error.
  4. The UPDI has now recovered from the Error state and is ready to receive the next SYNCH character and instruction.