| 摘要 |
PURPOSE:To operate the switches of a keyboard device safely and securely, by providing a capacitor which makes a current flow for a certain time when the power is supplied, a fixed resistor which is selected to reach a prescribed voltage a certain time later, and a level detector. CONSTITUTION:A capacitor 1 flows a current when the power is supplied and a resistor 2 is selected to reach a prescribed voltage a certain time later; and a level detecting circuit 3, when powered up, generates an output for a certain time. A switch scanning circuit 4 sends a signal only in the direction X of a keyboard 8 with time, and an encoder circuit 11 detects and encodes contact states in the direction Y of the keyboard 8. Then, an OR circuit 9 ANDs contact outputs in the direction Y, and an AND circuit 10 permits the AND output to pass itself only for the certain time of power feeding, and it is stored and held as a trigger signal for a holding circuit 12. For example, if some switch on the keyboard 8 is pressed abnormally during the power feeding, the circuit 11 is reset and other circuits are all stopped from operating. |
