A method and circuit provide a system level reset function for an electronic device. An initial reset function is provided under a low voltage condition of supply voltage, such as occur upon first energizing the electronic device. A tunable reset function is also provided, which can first be asserted at a voltage level setting less precise than that setting becomes upon tuning. Further, a boot-up reset function is provided, which provides its reset function at a voltage level setting that is set according to a calibration. Calibration can be based on data stored in a non-volatile memory, and can involve a checksum operation. The electronic device, a microcontroller for instance, is held in a reset state with any of the initial, tunable, and boot-up reset functions.