PURPOSE: To test an internal circuit without increasing the number of terminals by providing an inverter receiving a signal from an internal logic circuit at the input and a clamp circuit clamping the output of the inverter and leading out the inverter output from a signal terminal.
CONSTITUTION: When a signal A of high/low (GND) level is outputted from the 2nd logical circuit 3, the signal is inverted by an inverter 4 and the output is led to a signal terminal 1. A signal B, however, is clamped at a threshold level VF of a diode D, the range of the signal change does not exceed the threshold level of the 1st logical circuit 2. On the other hand, the signal B led out of the signal terminal 1 is checked by monitoring directly the waveform or amplifying the level up to a prescribed switching level by means of an external circuit. Thus, the signal of the internal circuit is tested by using a conventional input terminal.
SAWAMURA AKIRA
FUJII KIYOUGO
