Patent ID: 8364988

Claim:
A microprocessor comprising: a logic circuit including transistors and having a first mode and a second mode; a substrate bias control circuit changing a substrate bias voltage which is supplied to a well in which the transistors of the logic circuit are formed, and an operation mode control circuit operating in response to an execution of a first instruction which indicates to change to the first mode or a first interruption which indicates to change to the second mode, wherein the microprocessor receives a power source from a battery, wherein the operation mode control circuit controls the substrate bias control circuit in response to the first instruction so as to change the substrate bias voltage to a first voltage for the first mode in case that a voltage of the power source is lower than a predetermined voltage, wherein the operation mode control circuit controls the substrate bias control circuit in response to the first interruption so as to change the substrate bias voltage to a second voltage for the second mode, wherein the logic circuit is controlled in response to the first instruction so as not to change the input thereof in case that the voltage of the power source is lower than the predetermined voltage, wherein an absolute value of a threshold voltage of the transistors of the logic circuit that are supplied with the voltage for the first mode is higher than an absolute value of a threshold voltage of the transistors of the logic circuit that are supplied with the voltage for the second mode, and wherein the operation mode control circuit includes a timer to count a predetermined time in case that the substrate bias voltage changes from the first voltage for the first mode to the second voltage for the second mode.