I/O Lines and Connections

To operate the UPDI, the RESET pin must be set to UPDI mode. This is not done through the port I/O pin configuration as regular I/O pins but through setting the RESET Pin Configuration (RSTPINCFG) bits in FUSE.SYSCFG0, as described in UPDI Enable with Fuse Override of RESET Pin, or by following the UPDI high-voltage enable sequence from UPDI Enable with High-Voltage Override of RESET Pin. Pull enable, input enable, and output enable settings are automatically controlled by the UPDI when active.