| 摘要 |
PURPOSE: A method for selecting an input signal of a private automatic branch exchange and an apparatus thereof are provided, which select an input signal inputted to a PLL(Phase Locked Loop) and at the same time detect a frequency difference between signals in a frequency correction block. CONSTITUTION: According to the method, a plurality of input signals are counted together with an output signal frequency of an oscillator(S400), and then the counted value and a reference signal of a PLL(Phase Locked Loop) are compared(S401). A counted value of an input signal of a higher priority among the compared counted values is extracted(S402). It is judged whether the extracted counted value is separated from a pre-established reference range for a constant time(S403). If the extracted counted value is not separated from the pre-established range for a constant time, an input signal corresponding to the extracted counted value is transmitted(S404). An average value of the above counted values is calculated by counting the transmitted signal at every period.
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