Abstract: A semiconductor integrated circuit has an applied external voltage detector (3) which determines if a level of an applied external voltage (Vex) exceeds a threshold level. When the applied external voltage does not exceed the threshold voltage, an internal voltage selector (4) selects and outputs to a voltage drop circuit (10) a constant reference voltage which is generated and dropped from the applied external voltage by a reference voltage generator (1), based on an output of the applied external voltage detector. The voltage drop circuit generates and applies an internal voltage equal to the constant reference voltage, i.e. a dropped applied external voltage to internal circuit. On the other hand, when the applied external voltage exceed the threshold voltage, the internal voltage selector selects an aging voltage output from an aging voltage generator (2), based on an output of the applied external voltage detector.

Abstract: A resistor is connected to the source of a C-MOS inverter included within a crystal oscillator circuit in order to reduce the power dissipation in the crystal oscillator circuit. A switching transistor is connected in parallel to said resistor, said switching transistor being responsive to an LED display switch for enabling LED display or an illumination lamp switch for illuminating a liquid crystal display. The switching transistor shunts the resistor in response to actuation of the LED display switch or the illumination lamp.