| 摘要 |
PURPOSE:To make change-over of circuit functions possible without installing more external terminals of change-over for a test operation mode which are used, for example, only at the time of testing, by a method wherein a signal of, for example light, is received by a sensor and converted into an electric signal for change-over of circuit functions. CONSTITUTION:When a photo transistor 9 is not irradiated by a light, the OFF state is held and a control signal Ti is set as '1' at a connection point A. Then a third circuit 7 is connected to a first circuit 5, and an ordinary mode operation is performed. When the photo transistor 9 is irradiated by a light from the outside, it turns into the ON state, and the voltage of a power source VCC is divided by a load 10 and the ON resistance of the photo transistor 9. By setting suitably this voltage division ratio at the stage of circuit design, the control signal Ti='0' generates at the connection point A. As the result of this, a control signal C1 becomes '0'. When the control signal Ti is '0', it is inverted by an inverter, and the control signal C2 becomes '1'. So that the third circuit 7 is connected to the second circuit 6, and an test mode operation is performed.
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