ATMEGA8_14 Datasheet, PDF (153/331 Pages) ATMEL Corporation – High-performance, Low-power Atmel

ATmega8(L)
Examples of Baud
Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asyn-
chronous operation can be generated by using the UBRR settings in Table 60. UBRR values
which yield an actual baud rate differing less than 0.5% from the target baud rate, are bold in the
table. Higher error ratings are acceptable, but the Receiver will have less noise resistance when
the error ratings are high, especially for large serial frames (see “Asynchronous Operational
Range” on page 144). The error values are calculated using the following equation:
Error[%]
=


B_----a_----u_---d_----R_----a_---t_--e_{---C----l-o--s---e--s---t--M----a---t-c--h-}
BaudRate
–
1_
 100%
Table 60. Examples of UBRR Settings for Commonly Used Oscillator Frequencies
Baud
Rate
(bps)
f_osc = 1.0000MHz
U2X = 0
U2X = 1
UBRR Error UBRR Error
f_osc = 1.8432MHz
U2X = 0
U2X = 1
UBRR Error UBRR Error
2400
25
0.2%
51
0.2%
47
0.0%
95
0.0%
4800
12
0.2%
25
0.2%
23
0.0%
47
0.0%
9600
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
14.4k
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
19.2k
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
28.8k
1
8.5%
3
8.5%
3
0.0%
7
0.0%
38.4k
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
57.6k
0
8.5%
1
8.5%
1
0.0%
3
0.0%
76.8k
–
–
1
-18.6%
1
-25.0%
2
0.0%
115.2k
–
–
0
8.5%
0
0.0%
1
0.0%
230.4k
–
–
–
–
–
–
0
0.0%
250k
Max ⁽¹⁾
–
–
62.5kbps
–
–
125kbps
–
–
115.2kbps
–
–
230.4kbps
1.
UBRR = 0, Error = 0.0%
f_osc = 2.0000MHz
U2X = 0
U2X = 1
UBRR Error UBRR Error
51
0.2%
103
0.2%
25
0.2%
51
0.2%
12
0.2%
25
0.2%
8
-3.5%
16
2.1%
6
-7.0%
12
0.2%
3
8.5%
8
-3.5%
2
8.5%
6
-7.0%
1
8.5%
3
8.5%
1
-18.6%
2
8.5%
0
8.5%
1
8.5%
–
-
–
–
–
–
0
0.0%
125kbps
250kbps
2486AA–AVR–02/2013
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