| 摘要 |
PROBLEM TO BE SOLVED: To provide a communication cable system of a simple configuration connecting a portable telephone set to an external device so as to execute data communication between them, capable of easily and surely executing the mode switch of a portable telephone set while securing compatibility with various portable telephone sets. SOLUTION: This system is provided with converting circuits 4a and 4b for respectively converting the levels of incoming and outgoing serial data communicated between external equipment 2 and a portable telephone set 1 and a control circuit 4c for selectively grounding a control signal terminal CNT to be used for setting the conditions of switching the operating mode of the portable telephone set with switch operation while receiving a communication request signal, for example, to be outputted from the external equipment and further, the communication request signal is utilized as the power source of the converting circuit 4b.
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