Device for generating horizontal scanning periodic signal of pal-system to obtain clear display image

A device for generating a horizontal scanning periodic signal used for a PAL-system comprising:

• a clock generation means for generating a basic clock having a frequency specified as any multiple of a color subcarrier frequency;
• a counter means, connected to said clock generation means, for counting said basic clock until a specific clear signal is input;
• a first clear signal generation means, connected to said counter means, for generating a first signal when a value of said counter means is coincident with a normal horizontal scanning period, by monitoring the value of said counter means;
• a second clear signal generation means, connected to said counter means, for generating a second signal, when a value of said counter means is coincident with a longer horizontal scanning period by an odd multiple of a half period of the color subcarrier frequency than the normal horizontal scanning period, by monitoring the value of said counter means;
• and
• a selector means, connected to said first and second clear signal generation means and said counter means, for selecting one of the first signal and the second signal, wherein said second signal is at least one signal selected during one vertical scanning period.