JPS6469977A - Integrated circuit - Google Patents

Abstract

PURPOSE:To make an integrated circuit multi-functioning without increasing an external terminal, by a method wherein a signal such as a light given from outside is converted into an electric signal by a sensor to be used as an input signal to a specific combinational logic circuit. CONSTITUTION:In a test mode, i.e. at the time when a mode control signal T = 1, an input signal Si inputted to a combinational logic circuit 9 at the time of a normal operation is neglected by a 2-input AND circuit 6. When an optical signal LI is applied, a phototransistor (TR) 1 turns on, a voltage drop is caused by a load 2, and an 'L' signal is outputted therefrom. This signal is inverted by an inverter circuit 3, and &dH' signal is inputted to a 2-input AND circuit 5, and 'H' is obtained as an output. This signal passes through a 2-input OR circuit 7 and an output signal Di = 1 of a photosensing circuit 8 is outputted. When the optical signal Li is intercepted, the TR 1 turns off, and a supply voltage Vcc, i.e. 'H', is outputted through the load 2. This signal is inverted by the circuit 3, 'L' is inputted to the circuit 5 and passes through the circuit 7, and an output signal Di = 0 is outputted.