Interlacing Question

[Dr. Van Thorp]

A subject that has come up elsewhere on this forum is interlacing.

 

I have a technical question.

 

When you display an interlaced image on a computer of video game console, the image is sent to the TV in two peices. First the odd numbered scan lines are sent, then the even numbered scan lines. Then the proccess is repeated 30 times a second.

 

How does the TV set know which set of scan lines it is recieving at a given time? If they got switched, you would get a scrambled image.

 

Is there some difference on the sink signal, or some kind of signal sent at the end of the vertical blanking interval?

 

Thank you for whatever information you can provide.