Two mode scrambling system using identifier pulse in vertical blanking interval
US4611242A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 7, 1984 |
| Grant date | Sep 9, 1986 |
| Priority date | — |
| Expiry date | May 7, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/1675
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A cable television system capable of decoding signals encoded in two different formats, A and B. Format A is identified by digital data on horizontal lines 10-13 in the vertical blanking interval and format B by digital data on horizontal lines 14-17 in the vertical blanking interval. Logic circuitry receives the vertical blanking interval data and supplies one pulse marking the beginning of the vertical blanking interval and an identifier pulse derived from digital data on horizontal lines 13 or 17. A format mode control switch includes a monostable timing circuit producing an output responsive to the vertical blanking interval pulse for a period terminating at approximately horizontal line 14. The timing circuit output is supplied along with the identifier pulse to the inputs of a flipflop for determining which of the decoders A and B is to be energized.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.