| 摘要 |
PURPOSE: A key display circuit is provided, which uses an R-S flip flop to turn on a light emitting device connected serially to a control key. CONSTITUTION: A number of key switches(SW1,SW2,SW3,SW4) are operated by user selection. A number of display devices are allocated to the above key switches respectively. A number of flip flops(FF1,FF2,FF3,FF4) are allocated to the key switches respectively, and receive a selection signal of each switch as the first control input and signals of other key switches as the second input, and output the signal of the selected switch. And a number of driving devices are allocated to the flip flops respectively, and are operated by an output signal of each flip flop, and drive the display device. A switching diode is connected between the key switches and the second input of the flip flop.
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