The document discusses serial communication in the ATmega16 microcontroller. It describes the basics of serial communication including synchronous and asynchronous transmission. It provides details of the serial communication hardware in ATmega16 including the Universal Synchronous Asynchronous Receiver Transmitter (USART) module, baud rate registers, control and status registers, and data register. It also discusses initializing the serial port, sending and receiving characters through the USART.