Manual

64
AT90S/LS8535
1041H–11/01
Baud Rate Generator The baud rate generator is a frequency divider which generates baud rates according to
the following equation:
• BAUD = Baud rate
• f
CK
= Crystal 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. UBRR values that yield an actual baud rate dif-
fering less than 2% from the target baud rate are boldface in the table. However, using
baud rates that have more than 1% error is not recommended. High error ratings give
less noise resistance.
Table 24. UBRR Settings at Various Crystal Frequencies (Examples)
Note: Maximum baud rate to each frequency.
BAUD
f
CK
16(UBRR 1 )+
--------------------------------------=
Baud Rate
1MHz
%Error
1.8432 MHz
%Error
2MHz
%Error
2.4576 MHz
%Error
2400
UBRR=
25 0.2
UBRR=
47 0.0
UBRR=
51 0.2
UBRR=
63 0.0
4800
UBRR=
12 0.2
UBRR=
23 0.0
UBRR=
25 0.2
UBRR=
31 0.0
9600
UBRR= 6 7. 5 UBRR=
11 0.0
UBRR=
12 0.2
UBRR=
15 0.0
14400
UBRR= 3 7. 8 UBRR=
70.0
UBRR= 8 3.7 UBRR= 10 3.1
19200
UBRR= 2 7. 8 UBRR=
50.0
UBRR= 6 7. 5 UBRR=
70.0
28800
UBRR= 1 7. 8 UBRR=
30.0
UBRR= 3 7. 8 UBRR= 4 6.3
38400
UBRR= 1 22.9 UBRR=
20.0
UBRR= 2 7. 8 UBRR=
30.0
57600
UBRR= 0 7. 8 UBRR=
10.0
UBRR= 1 7.8 UBRR= 2 12.5
76800
UBRR= 0 22.9 UBRR= 1 33.3 UBRR= 1 22.9 UBRR=
10.0
115200
UBRR= 0 84.3 UBRR=
00.0
UBRR= 0 7.8 UBRR= 0 25.0
Baud Rate
3.2768 M Hz
%Error
3.6864 M Hz
%Error
4MHz
%Error
4.608 M Hz
%Error
2400
UBRR=
84 0.4
UBRR=
95 0.0
UBRR=
103 0.2
UBRR=
119 0.0
4800
UBRR=
42 0.8
UBRR=
47 0.0
UBRR=
51 0.2
UBRR=
59 0.0
9600
UBRR=
20 1.6
UBRR=
23 0.0
UBRR=
25 0.2
UBRR=
29 0.0
14400
UBRR=
13 1.6
UBRR=
15 0.0
UBRR= 16 2.1 UBRR=
19 0.0
19200
UBRR= 10 3.1 UBRR=
11 0.0
UBRR=
12 0.2
UBRR=
14 0.0
28800
UBRR=
61.6
UBRR=
70.0
UBRR= 8 3. 7 UBRR=
90.0
38400
UBRR= 4 6. 3 UBRR=
50.0
UBRR= 6 7. 5 UBRR= 7 6.7
57600
UBRR= 3 12.5 UBRR=
30.0
UBRR= 3 7. 8 UBRR=
40.0
76800
UBRR= 2 12.5 UBRR=
20.0
UBRR= 2 7. 8 UBRR= 3 6.7
115200
UBRR= 1 12.5 UBRR=
10.0
UBRR= 1 7.8 UBRR= 2 20.0
Baud Rate
7.3728 M Hz
%Error
8MHz
%Error
9.216 M Hz
%Error
11.059 M Hz
%Error
2400
UBRR=
191 0.0
UBRR=
207 0.2
UBRR=
239 0.0
UBRR= 287 -
4800
UBRR=
95 0.0
UBRR=
103 0.2
UBRR=
119 0.0
UBRR=
143 0.0
9600
UBRR=
47 0.0
UBRR=
51 0.2
UBRR=
59 0.0
UBRR=
71 0.0
14400
UBRR=
31 0.0
UBRR=
34 0.8
UBRR=
39 0.0
UBRR=
47 0.0
19200
UBRR=
23 0.0
UBRR=
25 0.2
UBRR=
29 0.0
UBRR=
35 0.0
28800
UBRR=
15 0.0
UBRR= 16 2.1 UBRR=
19 0.0
UBRR=
23 0.0
38400
UBRR=
11 0.0
UBRR=
12 0.2
UBRR=
14 0.0
UBRR=
17 0.0
57600
UBRR=
70.0
UBRR= 8 3. 7 UBRR=
90.0
UBRR=
11 0.0
76800
UBRR=
50.0
UBRR= 6 7. 5 UBRR= 7 6.7 UBRR=
80.0
115200
UBRR=
30.0
UBRR= 3 7. 8 UBRR=
40.0
UBRR=
50.0