How does the nintendo 3ds cash card work?

I was just wondering because the dsi has a nintendo points card for it and the 3ds has a cash card. So how does the cash card work for the 3ds? What's the difference?|||There is basically no difference. You go onto eShop, click on menu, and one of the things should say something like add more cash. Then, just click on add more cash using cash card (it will say something like this, not excatly), type in the code and buy.|||There really is no difference between them you enter in the code and you use it to buy games. Except one is for a DSi and the other is for the 3DS.