VHDL is very useful tool for designing digital circuit. The designed circuit is described in text format that look like high-level language programming. The described circuit can be edited and simulated unit it meets the desired specification. Then, the circuit can be automatically synthesized and implemented as specialized intregrated circuits or standard components automatically. Teletext is a kind of information service that can be broadcasted by television station. This service is currently provided in Thailand on TV Channel 5. Teletext signals are inserted between normal television signal frames. Hence they are not visible on ordinary TV sets. Viewing the teletext data needs a special device called teletext decoder. Through this device, the viewer has an option to view either a normal television program or a selectable text information page. This thesis describes the use of VHDL to design a very large digital circuit which is an important part of a Thai/English teletext decoder. It includes the main function of a microcontroller, Thai/English CRT controller, decoder and remote control in a single chip. To verify the design, a Thai/English teletext decoder was built assembling this single chip with the remaining analog parts such as tuner, video input processor and video former.
