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 for 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 12V enable sequence from UPDI Enable with 12V Override of RESET pin. Pull enable, input enable and output enable settings are automatically controlled by the UPDI when active.