| 摘要 |
A keyboard scan circuit in accordance with the present invention comprises a microprocessor (301) for scanning rows and columns of a matrix (300) of switchable elements. The scanning capacity of the microprocessor is increased in terms of the quantity of switchable elements the microprocessor may scan without increasing the number of ports or leads employed for scanning and without the use of a peripheral interface adapter circuit. In one embodiment of the present invention, one output port (307, 307A) of microprocessor (301) is connected in parallel to a central processor (308) and to the scanned matrix (300). A logic gate (309) is connected in parallel to at least two output leads (302A) of another port (302) of microprocessor (301). Logic gate (309) strobes the central processor (308) to read a code identifying a switched element at the parallel-connected output port (307, 307A). The central processor (308) otherwise ignores the presence of scanning signals at the parallel-connected output port (307, 307A). In an alternative embodiment, serial transmission of the code is accomplished by transmitting the code through the logic gate (309).
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