Hi @Richu-Bini, The Uart Baud Rate Register (UBRR) is used to set the clock for the UART shift registers and For standard crystal and resonator frequencies, the most commonly used baud rates for asynchronous operation can be generated by using the UBRR settings provided by the AVR Datasheet: AVR306: Using the AVR USART on tinyAVR and megaAVR devices
And you can find the equation from the datasheet to calculate the UBRR values depends on the clock source it has.
8422ea95-2844-483c-8e41-acab03c9ec41-image.png more details at the AVR306: Using the AVR USART on tinyAVR and
megaAVR devices
alt text src: http://www.avrbeginners.net/architecture/uart/uart.html#baud_generator
resource:
https://cache.amobbs.com/bbs_upload782111/files_22/ourdev_508497.html http://www.avrbeginners.net/architecture/uart/uart.html#baud_generator