Also the USART automatically senses the start of transmission of RX line and then inputs the whole byte and when it has the byte it informs you(CPU) to read that data from one of its registers.



The USART of AVR is very versatile and can be setup for various different mode as required by your application. In this tutorial I will show you how to configure the USART in a most common configuration and simply send and receive data. Later on I will give you my library of USART that can further ease you work. It will be little complicated (but more useful) as it will have a FIFO buffer and will use interrupt to buffer incoming data so that you are free to anything in your main() code and read the data only when you need. All data is stored into a nice FIFO(first in first out queue) in the RAM by the ISR.