| 摘要 |
PURPOSE:To easily discriminate the mode of NTSC/PAL by measuring the period of a vertical sync signal by a reference clock, and comparing it with a preliminarily set threshold. CONSTITUTION:The title device is provided with a cyclic counter 2 to count the reference clock CK, a RAM 7 to store a count value at every time when the vertical sync signal Vss arrives, an arithmetic operator 9 to calculate the period of the vertical sync signal according to the count value, and a ROM 8 to store a first threshold to distinguish the period of the respective vertical sync signals of NTSC/PAL system and a second threshold to distinguish the period shorter than the period of the vertical sync signal of the NTSC system. Then, when the period of the vertical sync signal is larger then the second threshold, a broadcasting system is discriminated according to the first threshold and the period of the vertical sync signal. Thus, the broadcasting system can be discriminated according to only the vertical sync signal. |
