| 摘要 |
PROBLEM TO BE SOLVED: To reduce current consumption by connecting a power source and the ground so as to output a DTMF signal from a prescribed node only when a control transistor is turned on and inhibiting the output of the DTMF signal by turning off the control transistor based on the detected result of a state not to perform speaking. SOLUTION: A microcomputer outputs the DTMF signal synthesizing two kinds of frequencies corresponding to the operation of a speak button on a telephone set. The microcomputer has a circuit composed of inverters 106-108, NAND gate 105 and NPN transistors 102 and 103 for connecting a power source VDD and a ground GND. In the state of canceling the reset of the microcomputer or resetting it, when there is no first and second standby state or there is any one of these states, the respective transistors are turned on or off. Therefore, the DTMF signal can be outputted or the output is inhibited just for the period from the operation start of an operate button to the end of speaking or in spite of that period. Thus, current consumption is reduced.
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