| 摘要 |
In a multimedia communication terminal, a CPU generates a mode identifier and subsequently a switching signal in response to a command input as well as in response to receipt of an incoming mode identifier. Frame synchronization circuitry multiplexes an outgoing digital video signal from a video codec with the mode identifier into an outgoing composite video signal, and demultiplexes an incoming composite video signal from a distant terminal into a mode identifier and a digital video signal. In response to the switching signal, the terminal is switched from video to data communication mode by coupling a LAPB (link access procedure balanced) controller to an ISDN (integrated services digital network) interface so that the CPU can exchange computer data and/or a mode identifier with the distant terminal without frame sync. Due to the elimination of frame sync, the terminal can access a database through the ISDN network. The terminal is switched from data to video communication mode by coupling the LAPB controller to the interface via the frame synchronization circuitry so that the video codec exchanges composite video signals with the distant terminal. During the video mode, the synchronization circuitry supplies an incoming data mode identifier to the CPU via the LAPB controller and the CPU supplies an outgoing data mode identifier to the synchronization circuitry via the LAPB controller.
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