ajax action to update/refresh multiple fields on the screen

Is there a way to handle (update/refresh) multiple fields in ajax action for a visible control. e.g. When user select/change a  value from drop down list, should update/refresh 3 other fields on the screen.

My suggestion is to have your callback function take care of the updates/refresh.

how to use it please give me an example to use it

i met a problem that is how to set selected option in activeDropDownList to activeTextField,how