68
ATmega103(L)
0945G–09/01
Baud Rate Generator
The baud rate generator is a frequency divider that generates baud rates according to
the following equation:
•
BAUD = baud rate
•
f
CK
= CPU clock frequency
•
UBRR = contents of the UART baud rate register, UBRR (0 - 255)
For standard crystal frequencies, the most commonly used baud rates can be generated
by using the UBRR settings in Table 24. Observe that CPU clock frequency can be
lower than the XTAL frequency if the XTAL divider is enabled. UBRR values that yield an
actual baud rate differing less than 2% from the target baud rate are in boldface in the
table. However, using baud rates that have more than 1% error is not recommended.
High error ratings give less noise resistance.
BAUD
f
CK
16 UBRR
1
+
(
)
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=