what is PAL-NC and how to set it

Hi all,

I am using my own software to grab images from the small black-white camera 
via the simple TV card (AverMedia TvGO) with BT848A chip on board. Using v4l 
API on linux kernel 2.4.20

My problem is that the grabbed image is whole black with some white lines 
(looks like divided into 16 small frames).

When I try it with xawtv I can see the same effect (for Composite1 channel). 
But when I swicht the TV norm in xawtv settings window to PAL-NC (from plain 
PAL) I can see the correct image. What is PAL-NC norm and how can I set it 
programatically using v4l API - I can't find way to do it.

thanks for any help
Jacek