The EM84502 Mouse Controller is specially designed to control PS/2 mouse device.This single chip can interface three key-switches and four photo-couples direct to 8042. EM84502 can receive command and echo status or data format which are compatible with IBM PS/2 mode mouse. Key debouncing circuit is provided to prevent false entry and improve the accuracy. In the conventional mouse, a great number of noises are generated when the grid is partially closed or opened. These noise are usually mistaken for movement signals by conventional mouse controller and the cursor of the dispaly screen is thus moved frequently up and down or back and forth. This will consumes a great amount of energy.The EM84502 PS/2 mouse controller provides noise immunity circuits to eliminate these noise in order to reduce energy consumption.