2 button interfacing with at89c51

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dear sir,.
i need how to push button use to increment&decrement decimal value(0 to 999) in lcd display using at89c51 micro controller.i want interface 3 pushbutton. 1st button pressing 2 or 3 sec ,after adjust one button to increase value,another button using decrement value.then press 1st button
this value wiil be constant. i need the circuit diagram & embedded c code.
pls help me.