| 摘要 |
A switching circuit for outputting input and output signals from a single terminal includes an I/O signal interface circuit for forming a current path in parallel with a switch when a voltage at both terminals of the switch changes from high state to low state and for opening the current path when receiving a delay signal. An I/O signal separator provides the delay signal of predetermined time width when forming the current path to the I/O signal interface circuit and for blocking the current path during the delay period. Repeated and consecutive striking of a singular switch is ignored since only the first strike is effective. In addition, a display connected to a previously pressed switch remains continuously lighted when an interval between two consecutive struck different switches is shorter than the delay period. By selectively coupling a number of I/O signal interface circuit and separator pairs, input and output terminals associated with function-selecting switching circuits can be reliably embodied in a single terminal construction. Such single terminal construction facilitates adding switches and displays, as necessary, without concern for an otherwise considerable increase in the number of input and output terminals. Additionally, the simplicity of a single terminal construction serves to significantly reduce the number of peripheral circuit components as compared to conventional switching circuits provided with a two terminal I/O construction.
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