The debugger does not mask any fuse bits or combinations when writing fuses. It is not possible to disable UPDI by fuse setting on devices with a dedicated UPDI pin. For devices with a shared/configurable UPDI pin, be sure not to select an alternate pin function for UPDI either by fuse setting in Programming mode or by using the I/O view or memory views to modify the memory-mapped fuse values. Disabling UPDI will render the debugger unable to contact the target device — an external programmer capable of 12V UPDI activation will be required.