Patent ID: 7873769

Claim:
A method of operating a micro controller unit comprising: maintaining a stop mode operation, using the micro controller unit, when a battery level detected in response to a first interrupt signal from an external source is in a predetermined low voltage level range during the stop mode operation; and performing a normal operation, using the micro controller unit, corresponding to a second interrupt signal from the external source without performing a reset operation, when a battery voltage level detected in response to the second interrupt signal is higher than a highest voltage level belonging to the predetermined low voltage level range, wherein upon receiving at least one of the first and second interrupt signals: turning on a low voltage detector in response to a respective received interrupt signal and detecting the battery voltage level supplied from the external using a turned-on low voltage detector; and turning off the turned-on low voltage detector and maintaining the stop mode operation, when the detected battery voltage level is in the predetermined low voltage level range.