| 摘要 |
PURPOSE:To prevent the block of a line due to an erroneous memory and to improve the availability of the device by automatically erasing the erroneous memory of a line number memory or a drop number memory generated by a manual operation or a single side changeover or the like. CONSTITUTION:The memory M storing a connection state stores connection information such as a connection destination line number through a selector S according to an inputted line number and information. When the changeover or a switch back of the line is newly carried out, the connection destination line number in this connection information is stored in a comparison part and the addresses of the memory M are successively generated, the contents of the memory in this memory are successively read and the read connection destination line number is successively compared with the connection destination line number stored by the comparison part C. When the same connection destination line number as the connection destination line number in the new connection information is found on other connection information different from the new connection information, an erasing signal is supplied to the memory M through the selector and the connection destination line number in other connection information is erased.
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