| 摘要 |
PURPOSE:To prevent data from being cleared intentionally or by mistake by providing another switch in a main device and inhibiting the data from being cleared unless the switch is set in a specific determined state. CONSTITUTION:The switch 34 for clearing prevention is provided to the main device 30, and even if a clear signal arrives from the key telephone set 40, the cumulative telephone charge stored in a register part 32 is not cleared by a central control part 31 as far as the switch 34 is on. Consequently, when the switch 34 for clearing prevention is turned on, the cumulative telephone charge stored in the register 32 are prevented securely from being cleared even if a clear signal is sent to a central control part 31 by pressing a key B on the key telephone set. |
