| 摘要 |
PURPOSE:To enable a microcomputer to execute other programs, by avoiding a keyboard service of the microcomputer, when all key contacts are opened. CONSTITUTION:Since a positive potential +V is given to reading lines r0-rn, when all key contacts are opened, all reading lines are fixed to a positive potential. In this case, since inputs of an NOR circuit 3 are all at positive potential, no output signal INT is generated. At this state, when a key contact, e.g., S01 is closed, the potential of the reading line r0 is lowered. Thus, the circuit 3 generates the output INT signal and a keyboard service is requested to a microcomputer. The microcomputer receives this request and rcognizes that the key contact connected to the reading line r0 is closed. When a driving signal is given to a driving line d1, a reading signal is generated on the reading line r0. Thus, the closing of a contact S01 at a crossing point between the lines d1 and r0 can be recognized. |
