Broadcast teletext system

• US 4,337,485 A
• Filed: 09/24/1980
• Issued: 06/29/1982
• Est. Priority Date: 10/31/1979
• Status: Expired due to Term

• Current Assignee: Magnachip Semiconductor Limited (Magnachip Semiconductor)
• Original Assignee: British Broadcasting Corporation
• Inventors: Chambers, John P.
• Primary Examiner(s): Richardson, Robert L.
• Application Number:
  US06/190,470
• Time in Patent Office: 643 Days
• Field of Search: 358/142, 358/146, 358/146
• US Class Current: 348/467
• CPC Class Codes: H04N 7/0882 for the transmission of character code signals, e.g. for teletext circuits for the digital non-picture data signal H04N7/035

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. Whenever a receiver is switched on or to a channel carrying teletext, the decoder automatically responds to this line to acquire the addressed title page.

Claims

1. In a method of broadcast teletext transmission wherein information is transmitted as pages, comprising the steps of

transmitting, for each page, a plurality of rows of information forming a set of rows intended for display, at least one of said rows containing a digitally coded page address;

and

further transmitting, for at least some pages, an additional row of information outside said set of rows and not intended for display, said additional row containing one or more codes pointing to another page address.

2. In a method according to claim 1 wherein said pages are grouped in a plurality of N magazines and the one or more codes in said additional row which point to said another page address correspond to a page number which, when added modulo-N to the current magazine number, yields a new magazine number.

3. In a method according to claim 1 or 2 and further comprising the step of

periodically transmitting a further additional row of information, lying outside said set of rows and not being intended for display, said further additional row not being related to any specific page and containing coded information identifying at least one page.