PURPOSE:To secure stabilized circuit operation as well as to decrease the parts number by giving only the output corresponding to 2 to OR circuit and then by utilizing the output as the strobe signal.

PURPOSE:To monitor key operation effectively by taking out the outputs of X and Y axis as parallel binary codes respectively and detecting whether the key operation is single operation or not on the basis of a value indicated by the codes. CONSTITUTION:If plural keys are simultaneously depressed at the time of key operation, at least the outputs of one axis out of respective axial outputs X1- X4, Y1-Y3 are simultaneously overlapped and turned to ''1'' and any one of inputs to at least one of encoders ENC1, ENC2 is turned to ''H''. Therefore, all outputs D1-D8 from at least one of the encoders ENC1, ENC2 are kept at ''L''. Outputs from at least one of NAND gates G1, G2 are kept at ''H'' and outputs from at least one of EXOR gates G5, G6 are trned to ''H'' and sent as an overlapped signal DD through an OR gate 7. Consequently, whether the key operation is single operation or not is detected and the key operation can be monitored effectively.

Double keying prevention circuit

Citations

Key operation monitoring system

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