Atmel AT89S52 microcontroller, specifically the AT89S52-24PU model.
It is a low-power, high-performance CMOS 8-bit microcontroller.
It features 8K bytes of In-System Programmable (ISP) Flash memory.
The device operates with a supply voltage between 4.0V and 5.5V.
This chip is commonly used by hobbyist developers for building custom electronic projects.