| 摘要 |
PURPOSE:To prevent the misoperation of an equipment by detecting the depression state of a key of a keyboard which becomes faulty at the time of power-ON operation and to reduce the harmonic disturbance which is generated during scanning operation. CONSTITUTION:The key scan circuit is provided with a key scan control circuit 40 which inputs a POR signal at the same time with the power-ON operation. This key scan control circuit 40 receives the POR signal and outputs a control signal S2 for starting key-scanning operation to a key scan pulse generating circuit 50. Further, this key scan control circuit 40 outputs a control signal S3 for stopping the scanning operation to the key scan pulse generating circuit 50 a set time later. The key scan circuit forcibly performs the scanning operation with those signals S2 and S2 right after the power source is turned ON to detect a fault of a key switch in a key matrix 10. |
