Research And Implementation Of Closed Caption Display On DTV

Closed Caption Display is an important part of Digital Television System. By the standard encoding process, valid Closed Caption characters are inserted into either NTSC television signal or ATSC bit stream. Closed Caption decoder, involved in TV set or merely an independent set, can interpret those characters. At present, there are two protocols used to describe the standard encoding process: one is EIA/CEA-608-B, mainly used in analog television system; the other is EIA-708-B, mainly used in digital television system.Closed Caption Display is based on the digital television software design in RaisingSun Digital Video Technology (Shanghai) Co., Ltd.. The dissertation accomplishes decoding, controlling and displaying of Closed Caption module. The television system can receive and process both digital and analog television signal, so that Closed Caption module should be capable of collecting and interpreting Closed Caption data from either digital or analog stream.The dissertation implements decoding module to decode Closed Caption stream coded according to the protocols of EIA/CEA-608-B and EIA-708-B, and trans-code data coded by EIA/CEA-608-B to control characters defined by EIA-708-B, which the available displaying module could only deal with at present. Controlling module realizes to control data collection process, decoding process, messages sent to displaying module, and running status of Closed Caption. Displaying module realizes to process the messages, interpret and display characters, and respond to user settings.In addition, the dissertation studies on the relation between Closed Caption module and other modules in television system, including channel change module, Vchip module and OSD module.Through debugging and test, Closed Caption data can be normally displayed, and most displaying effects defined in protocol are realized.