They keep changing based as MCap changes but these changes are induced by IISL and not by the market. You may find some more here Index concepts from NSE site but it does not contain all. You can download the weights from there - Index weights, select the appropirate option from the drop down box. The best way I have understood them is to imagine you have one stock of each constituent, which is weighted by the weights, this gives you a figure. This figure is now multipled by a constant - not known or shared, that gives the Nifty. So if the stock falls by x% the index will fall proportionate to its weight but the weight itself will not change.
NSE website says that IISL (a sister company tasked with such indices) reviews it twice a year. That is what I have seen but in certain cases it is changed even in between. The one example is when Satyam, a part of Nifty, collapsed after the MD declared he committed fraud. Changes in India have been quite frequent like 4 - 5 firms every year, whereas the Dow has changed only 51 times since 1896!
It is cell H56 / G56. I copied some of these as values instead of formulae which is why you see it as values (I will retain it henceforth)