How to get zero crossing for a vector and the values of each crossing?

I have a signal generator and it displays square wave , now there are 4 channels and for each channel i need to plot the zero-crossings of the waves. I need a function/code to plot the data on the figure and need to get the data also as when the wave crossed zero point during its sampling. How to do that? For instance i have chA vector for channel A and it contains upto 1 million of samples. I need the values of the black marked places through out the sample. I am new to matlab, help will be appreciated.

thanks in advance.

Answer 1

[Jayanta Deb]

Now i have attached the matlab file you can find everything there. i need to have the zero crossign indexes and the values for those indexes. see what i am getting now after i plot your piece of code. none of the points are zero though they are closer to zero. please also refer the screenshot i gave you above.