| 摘要 |
PURPOSE: A circuit for keypad is provided to prevent the perating error by securing margin by a key operation as input voltage switching by pull up resistance of an input port at a key pad. CONSTITUTION: A key pad circuit comprises input port1 and input port2 connected to a first and a second pull up resistors(1,1a), respectively, an output port1 and an output port2 connected to a first and a second NMOS transistors(NMOS1,NMOS2), respectively, a first and a second inverters(INV1,INV2) connected in parallel between the input port1 and the first pull up resistor, and between the input port2 and the second pull up resistor(1a), respectively, a third and a fourth inverters(INV3,INV4) connected to gate of the first and the second NMOS transistors, and a key pad block consisted of the combination of the input ports and the output ports. The key pad circuit more comprises a first and a second falling edge detectors(4,4a) detecting the falling edge from output signals of the third and the fourth inverters, a first logic gate block(5) performing logic operation about the output of the first and the second falling edge detectors(4,4a), and a first and a second transistors(3,3a) being controlled by an output signal of the first logic gate block and being connected in parallel to the first and the second pull up resistors(1,1a).
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