| 摘要 |
PURPOSE: A method for switching ISDN synchronizing clock of a key phone is provided to reduce the manufacturing cost of the key phone by detecting clock synchronization between ISDN boards without a clock control cable. CONSTITUTION: A main board is initialized(S1). The main board periodically detects state information confirming active state of each ISDN board, from each ISDN board(S2). The main board saves individual state information inputted from each ISDN board at a memory(S3). The main board grasps state information transmitted from each ISDN board for selecting the currently activated ISDN board, and synchronizes clocks of each ISDN board through the selected ISDN board(S4). It is determined whether the currently activated ISDN board becomes non-activated(S5). If non-activated, a newly activated ISDN board is selected.
|
