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Received data is read from the Receive data buffer register (RXB). v. UBRRH & UBRRL (USART Baud Rate Registers.
This is the USART Baud rate register, it is 16BIT wide so UBRRH is the High Byte and UBRRL is Low byte. But as we are using C language it is directly available as UBRR and compiler manages the 16BIT access. This register is used by the USART to generate the data transmission at specified speed (say 9600Bps). To know about baud rate see the previous tutorial. UBRR value is calculated according to following formula.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register.