Ajax在控制器中调用php函数

I am using the below jquery code to call a ajax function in my contorller CS. Search is the function name. How ever the function is called in the controller. But i am supposed to get a value in the text box of the page inside this function. Basically this is for the auto complete feature. on key up the function is called. But i am not able to get the value in the textbox to do a relavent search. please reply back anything you feel would be helpful to me. Thanks in advance. I am using the below jquery code to call a ajax