| 摘要 |
<p>PURPOSE: To speedily and precisely detect the abnormality of an ST2 signal before data begin to be transmitted. CONSTITUTION: When an ST2 signal is normally inputted to the full-wave rectifying circuit 151 of an abnormality detecting circuit, the ST2 signal is rectified on a full-wave basis and a current flows from the side of a capacitor C to a light emitting diode D5 through a resistance R1, so that this diode D5 illuminates. Consequently, a phototransistor T turns on and a detection signal as its collector voltage goes down to a low level, indicating that the ST2 signal is normal. If the ST2 signal is continuously at the low level owing to an open circuit, the voltage on the side of the capacitor C becomes zero and the current supply to the light emitting diode D5 is ceased to disable the light emitting diode D5 to illuminate, so the phototransistor T turns off and the detection signal as its collector voltage goes up to a high level, thereby informing the CPU of an data terminal device, unshown in the figure, of the abnormality of the ST2 signal before data transmitting operation.</p> |
