| 摘要 |
PURPOSE:To secure the secret of contents of registered data by limiting the function of a program only to the registration and deletion of data and discrimination whether data have been registered or not. CONSTITUTION:When a switch circuit 400 to be switched connects a connection 610 to a connection 620, normal driving state is obtained. In case of the periodical maintenance or the like of an electronic exchange, the switch 400 connects the connection 610 to a connection 630. When detecting the connection of the 610 with the 630, a data register 300 answers that all passwords have been registered to the inquiry and neglects a registration request and a deletion request. Consequently, data can be prevented from being registered or deleted in error or for fun. When the connection 610 is connected to 640, all the registered data are deleted. Since the data register 300 has a non-volatile storage circuit, data in the data register 300 can be held even at the failure of a power supply.
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