New multi-language computer controlled teletext decoders for 525 and 625 line systems

摘要

A range of multilanguage teletext decoders are described that can cover much larger geographical areas than before. These are known as enhanced computer-controlled teletext (ECCT), and several variants are available for different geographical areas. A character read-only memory (ROM) with 192 high-resolution characters is included on-chip, together with a more flexible ROM addressing mechanism to take full advantage of the multilanguage capability. Some areas require more than one language to appear on the screen simultaneously, other areas have different technical requirements, for example, 625- or 525-line transmission. The design of the teletext decoder to accommodate these requirements is discussed, together with the associated transmission aspects.