Fuses are part of the non-volatile memory and holds factory calibration data and device configuration. The fuses are available from device power-up. The fuses can be read by the CPU or the UPDI, but can only be programmed or cleared by the UPDI. The configuration and calibration values stored in the fuses are written to their respective target registers at the end of the start-up sequence.
The content of the Signature Row fuses (SIGROW) is pre-programmed, and cannot be altered. SIGROW holds information such as device ID, serial number, and calibration values.
The fuses for peripheral configuration (FUSE) are pre-programmed, but can be altered by the user. Altered values in the configuration fuses will be effective only after a Reset.
This device also provides a User Row fuse area (USERROW) that can hold application data. The USERROW can be programmed on a locked device by the UPDI. This can be used for final configuration without having programming or debugging capabilities enabled.