Broadcast teletext system
US4337485A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 24, 1980 |
| Grant date | Jun 29, 1982 |
| Priority date | — |
| Expiry date | Sep 24, 2000 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/0882
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Each broadcast page contains a row such as row 29 which is outside the set of displayed rows. In addition to the standard initial bytes CR (clock run in), FC (framing code) and MRAG (magazine number of 3 bits and row number of 5 bits), there are 4 bytes allocated to a 16-bit cyclic rundancy check code CRC for the page and 6 groups, of 6 bytes each, NEXT 0 to NEXT 5. Bytes are Hamming coded and thus contain only 4 message bits. Each 6-byte group is a pointer to another page address made up of page tens and page units (4 bits each), hour code tens and units (2 bits plus 4 bits) and minute code tens and units (3 bits plus 4 bits). The three spare bits from the tens bytes for hours and minutes contain a number which is normally 0 but, if not 0, is added modulo-8 in the decoder to the current magazine number in MRAG to derive the magazine number for the `next` page. A decoder equipped with a multipage store can respond to the pointers to acquire a sequence of pages automatically, all available immediately to the viewer. A specific line, not related to any particular page, say magazine 8 row 30, can be transmitted say once a second and includes a 6-byte group addressing a title page. Whe…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.