[quote="TEHb"]"The down-counter, running at system clock
(fosc), is loaded with the UBRRn value each time the counter has counted down to zero or when
the UBRRLn Register is written. A clock is generated each time the counter reaches zero."

Но, далее - в описании регистра:
"Writing UBRRL will trigger an immediate update of the baud rate prescaler."

То есть - новое значение будет загружено немедленно.[/quote]