This part is a kind of semiconductor called OM21PS.

Function of this product has Optical Mouse IC.

Manufacturers : ETC

Image and pinout :

Some of the text within the PDF file :

OM21PS Product Specification DOC. VERSION 1.0 Contents 1 2 3 4 5 6 7 8 9 10 General Description 1 Features ... 1 Pin Configurations (Package). 2 Functional Block Diagram .. 3 Pin Description 3 Absolute Maximum Rating. [ ... ]

OM21PS PDF Datasheet Download