33.2.5 I/O Lines and Connections

The UPDI uses the UPDI pin for half-duplex UART communication.

The RESET pin can be used to invoke and maintain UPDI operation.

The RESET pin can be used as RESET or input, depending on the configuration of the RSTPINCFG bit in the Pin Configuration (FUSE.PINCFG) fuse. The UPDI pin can be used as GPIO or for UPDI function, depending on the configuration of the UPDIPINCFG bit in the Pin Configuration (FUSE.PINCFG) fuse. The high voltage applied to the RESET pin can be used to invoke and maintain UPDI operation, thus overriding both pins configuration in the Pin Configuration (FUSE.PINCFG) fuse.

Refer to the UPDI Enabling section for details about the required and optional pin configurations.