PageUP/PageDown logic on a screen.

I need to populate 5 records each time when I hit page up or page down button. In last page the DOWN button should not work and in first page the UP button should not work. I have all the data of the contenta of the screen in an internal table in PBO of screen. Can anyone help me out the logic for populating this data on the screen based on page down/up buttons. Step loop is being used on the screen for population.

Thanks