| 摘要 |
This invention provides a central processing unit having read only memory for storing permanently the firmware and random access memory for storing the protocol which can be changed by user via the keyboard when need, which also has a detector for counting the ring signal inputted from the line and sending it to the CPU. When the count of the ring signal and the interval between the hang-up and dial are all met, the protocol stored in the RAM of the CPU and the control device enabled by the CPU via the output terminal send the tone signal to the ring apparatus for signaling the user.
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