Second generation teletext and viewdata decoders

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Abstract
The architecture of second generation hardware for teletext and viewdata decoding, System 12, is shown as an evolutionary progression of industry's experience and needs. The new architecture is described with emphasis on its application to data sources other than teletext, e.g. viewdata and cassette text. The (AI2L) technology strength which allowed such a system is also described, together with some commercial and technical reasons for its choice. Speed-power products in the order of 0.5 pJ, and delays of about 15 ns for a 5-collector gate, are achieved in production at a circuit density, and process complexity comparable to the most up-to-date m.o.s. processes in industry without the complexity of iterative design. Two of the newer devices that greatly increase system capability are described in greater detail. The remote control interface chip, SN76926, integrates System 12 to Texas Instruments Ltd.'s Mistic family of t.v. peripherals, which includes a low cost, 64-channel remote control. The bus system used also allows communication with Texas Instruments microprocessors. The other circuit described in detail is the system controller, i.e. SN76924, which allows microprocessors handling data to delegate to it a large proportion of the total task of communicating with System 12. Two-way interchange of information with System 12 is so far eased as to allow very low cost, 4-bit microcomputers to cope with major data handling functions. The technical and commercial maturity of product reached by this system gives UK teletext and Prestel services a substantial leadership which should be difficult to ignore if other factors do not retard the speedy development of the market

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