Baud rate generator – Rainbow Electronics AT90S2313 User Manual
Page 47
47
AT90S2313
0839I–AVR–06/02
• Bit 1 – RXB8: Receive Data Bit 8
When CHR9 is set (one), RXB8 is the ninth data bit of the received character.
• Bit 0 – TXB8: Transmit Data Bit 8
When CHR9 is set (one), TXB8 is the ninth data bit in the character to be transmitted.
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
= 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 15. UBRR values that yield an actual baud rate dif-
fering less than 2% from the target baud rate, are boldfaced in the table. However, using
baud rates that have more than 1% error is not recommended. High error ratings give
less noise resistance.
Table 15. UBRR Settings at Various Crystal Frequencies
BAUD
f
CK
16(UBRR
1)
+
-------------------------------------
=
Baud Rate
1 MHz %Error
1.8432 MHz %Error
2 MHz %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=
7
0.0 UBRR=
8
3.7 UBRR=
10
3.1
19200 UBRR=
2
7.8 UBRR=
5
0.0 UBRR=
6
7.5 UBRR=
7
0.0
28800 UBRR=
1
7.8 UBRR=
3
0.0 UBRR=
3
7.8 UBRR=
4
6.3
38400 UBRR=
1
22.9 UBRR=
2
0.0 UBRR=
2
7.8 UBRR=
3
0.0
57600 UBRR=
0
7.8 UBRR=
1
0.0 UBRR=
1
7.8 UBRR=
2
12.5
76800 UBRR=
0
22.9 UBRR=
1
33.3 UBRR=
1
22.9 UBRR=
1
0.0
115200 UBRR=
0
84.3 UBRR=
0
0.0 UBRR=
0
7.8 UBRR=
0
25.0
Baud Rate 3.2768 MHz %Error
3.6864 MHz %Error
4 MHz %Error
4.608 MHz %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=
6
1.6 UBRR=
7
0.0 UBRR=
8
3.7 UBRR=
9
0.0
38400 UBRR=
4
6.3 UBRR=
5
0.0 UBRR=
6
7.5 UBRR=
7
6.7
57600 UBRR=
3
12.5 UBRR=
3
0.0 UBRR=
3
7.8 UBRR=
4
0.0
76800 UBRR=
2
12.5 UBRR=
2
0.0 UBRR=
2
7.8 UBRR=
3
6.7
115200 UBRR=
1
12.5 UBRR=
1
0.0 UBRR=
1
7.8 UBRR=
2
20.0
Baud Rate 7.3728 MHz %Error
8 MHz %Error
9.216 MHz %Error
11.059 MHz %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=
7
0.0 UBRR=
8
3.7 UBRR=
9
0.0 UBRR=
11
0.0
76800 UBRR=
5
0.0 UBRR=
6
7.5 UBRR=
7
6.7 UBRR=
8
0.0
115200 UBRR=
3
0.0 UBRR=
3
7.8 UBRR=
4
0.0 UBRR=
5
0.0