Patent ID: 7873854

Claim:
A single chip microcontroller unit, comprising: a processing unit having a normal power mode of operation and a low power mode of operation; analog circuitry connected to the processing unit; digital circuitry connected to the processing unit; a power management unit controlling power operation of the processing unit, the analog circuitry and the digital circuitry; and a system voltage monitoring circuit for generating a system voltage control signal to maintain the power management unit in a reset mode responsive to a system voltage level with respect to a predetermined level during start-up of the single chip microcontroller unit, wherein the system voltage monitoring circuit further comprises: first control circuitry for generating a power on reset signal to maintain the power management unit in a reset state responsive to a determination that the system voltage level does not exceed the predetermined level; and second control circuitry for generating an indication whether the system voltage level exceeds the predetermined level responsive to the power on reset signal, an uncalibrated voltage detection signal and a calibrated voltage detection signal.