| 摘要 |
PURPOSE:To prevent the transferring of unnecessary information to a CPU by neglecting the information when the time from the previous change point is within a reference time specified beforehand and informing at the time of exceeding the reference time, when line information is changed. CONSTITUTION:When the line information at this time is inputted to a digital line controller 3 through a line information transmission line 6, the information is inputted through a line signal receiving circuit 31 to a comparator 32, a sending circuit 37, etc. The circuit 32 compares the input information with the previous line information from a register 36, and at the time of non- coincidence, outputs a non-coincident signal (b) to a counting circuit 34. Thus, the circuit 34 sends the counted value up to the previous time to the sending circuit 37, the circuit 37 compares the counted value with the reference value counted value set separately, when the value is smaller than the reference counted value, decides that the digital line is abnormal and the line information at this time is not sent to the CPU. On the contrary, at the time of exceeding the reference counted value, the line information at this time is effective and sent to the CPU. Consequently, the transfer of the unnecessary information to the CPU can be prevented.
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