The EM83702 Mouse Controller is specially designed to control mouse device. This single chip can interface three key-switches and four photo-couple direct to RS-232C. The EM83702 does not need any external power supply,so the mouse can go without a power line. It is versatile with both microsoft and mouse system. Debouncing circuit were provided to prevent false entry and to improve the accuracy. In 1200 baud rate non-auto speed with 200 DPI wheels and photo-couples, the scanning is 650 mm/sec without missing a dot in microsoft mode,and the scanning speed can up to 770 mm/sec in mouse system mode.