| 摘要 |
PURPOSE:To easily determine an access number without any error by providing a display bit for channel in-use display on an extension bus from a main device to a digital telephone set. CONSTITUTION:The digital telephone set 5 connected to the extension bus determines the positions of each signal channel 7 and a channel in-use state display channel 8 in frame synchronism with a frame channel 6. The digital telephone set 5 having detected the channel in-use state display channel 8 can access an unused signal channel by monitoring a channel in-use state display bit 9 to detect the in-use or disuse state of a signal channel on the extension bus. Consequently, an access channel on the extension bus can be set automatically according to the channel in-use state and a signal channel to be accessed is easily and accurately determined.
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