33.3.1.3.1 SYNCH in One-Wire Mode

The SYNCH character is used before each new instruction. When using the REPEAT instruction, the SYNCH character is expected only before the first instruction after REPEAT.

The SYNCH is a known character which, through its property of toggling for each bit, allows the UPDI to measure how many UPDI clock cycles are needed to sample the 8-bit SYNCH pattern. The information obtained through the sampling is used to provide Asynchronous Clock Recovery and Asynchronous Data Recovery on reception and to keep the baud rate of the connected programmer when doing transmit operations.