There is video of two kinds of MPEG2 in the transmission interface of current DVB-C system equipment code shedding transmits interface standard: Asynchronous is serial interface ASI and SPI of synchronous and collateral interface.
SPI altogether has 11 useful signal, every signal poor cent is used into two signal raise transmission interference rejection quality, transmit with DB25 on physical link, because this connects a line much and complex, transmission distance is short, appear easily breakdown. But SPI is collateral 11 signal, processing is simple and expansibility is strong, the input of the output of because this is current general MPEG2 video coder and video decoder is SPI interface signal of the standard.
ASI is used serial transmit, need a coaxial cable to transmit only, connect a line simple, transmission distance is long. According to the actor defect with SPI and respective ASI, often want to have the mutual transition of SPI and ASI interface when transmission signal.
1, SPI signal structure
SPI of collateral transmission system includes signal of signal of a clock, 8 data signal, a frame synchronization and a data effective signal. The synchronous byte 047H that TS of correspondence of frame synchronization signal wraps, effective signal uses data the length that divisional TS includes is 188 byte or 204 byte. When TS bag grows 188 byte, effective signal is data all the time tall n, at the same time all signal keep synchronous with clock signal.
2, ASI interface
ASI is transmitted stream can have different data rate, but transmission rate is constant, for 270Mbps, because this ASI is OK,be sent and receive the MPEG2 data of different rate. ASI transmission system is statified structure. ISO/IEC 13818 of standard of the 2nd top layer, use MPEG2 - 1 (SYSTEM) , the 0th mixes the 1st is the FC fiber channel that is based on 1SO/IEC CD 14165-1. FC supports a variety of physics to transmit agency, if coaxial cable is transmitted,wait.
The 8bit that will include synchronous MPEG2 deferent package above all piles up a word to be changed into 10bit to pile up a word; Be in then and / when stringing together changeover, input a new word when the requirement, and when data source has not gotten ready, should insert a K the synchronous word of 28.5, transmit rate in order to achieve the fixed 270Mbps of ASI. Forms serial bit flows will pass amortize / drive circuit and coupling network, send to coaxial cable connector. Should arrive at sink through coaxial cable, in receive when receiving data, want to pass connector and coupling network above all, coupling arrives on the circuit that restores clock and data, undertake stringing together next / alternate; To restore byte synchronism, ASI decoder must seek K28.5 synchronous word first, once search this synchronism word, it is the data demarcate that receives subsequently namely attrib border, built decoder to output the correct byte of byte to arrange thereby; Undertake 10/8bit alternates finally, the MPEG2 TS code that restores synchronism giving a package sheds data. But K28.5 synchronous word is not available data, because must be deleted when this decipher.
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