| 摘要 |
PURPOSE:To facilitate coping of the titled device with increase/decrease of key number of lots of kinds of telephone sets by providing the expanding mode operation and the non-expanding mode operation for the detection of key to the operation of key detection section and performing the setting by an external input change. CONSTITUTION:When a key scan signal is outputted from an output port 1 and a key is depressed, a signal is applied to an input port 2 connected to the depressed key and a telephone control IC discriminates the key depression. Moreover, a decoder 4 is provided to an external circuit, which is operated to expand the said key scan. In the case of selecting the external setting input as 'decode', the control IC inputs it with the power turned on and outputs a signal expanding the key scan signal. Thus, the expansion of the key scan signal is executed by the change in the external setting only and the setting change in the expansion mode of the key detection and the non-expansion mode is attained.
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