| 摘要 |
PURPOSE:To eliminate flickering on a screen during scramble system switching by switching descramble circuits in a vertical blanking period. CONSTITUTION:A center side switches scramble systems at constant intervals of time so as to prevent TV from being viewed by an illegal method. Consequently, a terminal side decodes a data signal indicating the switching of the scramble systems by a microcomputer part 17 and switches scramble circuits by a selecting circuit 14. Here, switching signal data is sent out in a vertical blanking period simultaneously with the scramble system switching so as to prevent a flicker on the screen, but if the microcomputer part 17 takes a time for the processing, descramble switching exceeds the vertical blanking period to generate flickering on the screen. In this case, a convention is so fixed that the data signal indicating the switching of the scramble systems is processed specially preferentially so as to prevent the flicker. |
