| 摘要 |
PURPOSE:To diagnose periodically and automatically whether an interface circuit is normal or not by supplying an on-test and an off-test signal as input signals by a test control circuit, and checking the present output of the interface circuit. CONSTITUTION:A latch circuit 2 is placed in a latch state in on-test mode to hold the current signal and a gate circuit 4 is opened to sent test data to a test data checking circuit 5. Then, light emitting diodes LED1 and LED2 are turned on, phototransistors PT1 and PT2 are activated, and a light emitting diode LED 3 is turned on. Consequently, a phototransistor PT3 turns on and its signal is inputted to the test data checking circuit 5 through an NOT circuit 3 and the gate circuit 4. The light emitting diode LED 2 is turned off in off- test mode, and the phototransistors PT2 and PT3 are turned off to input the signal to the test data checking circuit. |
