| 摘要 |
PURPOSE:To enable to detect channel switching, of a receiving set main body at a separated character broadcasting decoder side by checking the number and position of horizontal period in which character broadcasting is transmitted, and when these results are changed, clearing a memory for display of the character broadcasting decoder. CONSTITUTION:A program which is executed every time when 21st horizontal period is finished is added to an ROM12 of the character broadcasting decoder 10 at each field period, and the first group of counters CNTM and the group of flags FLGM are set to an RAM13 as shown in the figure A. Further, the second CNTN, FLGN and a change-over flag SWF and a counter V are set to the RAM13 as shown in the figure B. Further, a channel flag CHF is set to the RAM13 or an external latch. Thus, groups of flags FLGM, FLGN that detected the number or position of horizontal periods in which character broadcasting signals are transmitted out of 10th-21st horizontal periods are obtained. By comparing these, the presence of channel switching is judged by a flag CHF. A character broadcasting picture is erased at the time of switching. |
