Digital interface circuit in light synchronous digit transmission system and its data demultiplexing method

The invention relates to a digital interface circuit and the data demux method in optical synchronous digital transmission system. The interface circuit includes a data multiplexing model and a data demultiplexing. The data multiplexing model multiplexes the data, data with preset quantity are multiplexed into a state instructing signal, selects the correspondent time sequence of transmitting data and clock, sends out the warning information of interface configuration of the CPU, it also includes a clock edge generating sub-model, transmitting sequence counting sub-model, transmitting sequence selecting sub-model, warning and sequence configuration sub-model, data multiplexing sub-model. The invention designs the data definition sub-model, creates a data definition state machine, and provides a demultiplexing method for interface data, it increases the stability and tolerant of data restoration, weakens the affection to data restoration by the level fluctuation of the system.