| 摘要 |
PURPOSE:To prevent a keyboard device from misinput even if three keys are simultaneously depressed and to produce the keyboard device economically by executing the storage and transfer of keyed state every scanning of a keying means by a scanning device. CONSTITUTION:A keyboard input device is provided with an one-chip microprocessor 12, a ROM13, a RAM14, a timer 19 a serial port 20, and I/O ports 21, 22. The RAM14 includes a buffer memory 4, a last look memory 6 and row and line registers 8, 9. The I/O ports 21, 22 consist of 8 bits respectively and the key depressed information of a selected row is inputted to the input port 21. A diode 23 prevents the device from the inflow of current from the output ports 22 corresponding to unselected rows. Whether the total number of depressed keys is three or less is decided on the basis of the key depression information stored in the buffer memory 4, and in case of three or less, key accepting processing is executed by referring the contents of the memories 4, 6.
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