For standard crystal and resonator frequencies, the most
commonly used baud rates for asynchronous operation can be generated by using the UBRRn
settings as listed in the table below.
UBRRn 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 also section Asynchronous
Operational Range). The error values are calculated using the following
equation:
Error[%] = (BaudRateClosest MatchBaudRate−1)2 100%
Table 1. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
| Baud Rate [bps] |
fosc = 1.0000
MHz |
fosc = 1.8432
MHz |
fosc = 2.0000
MHz |
| U2Xn = 0 |
U2Xn = 1 |
U2Xn = 0 |
U2Xn = 1 |
U2Xn = 0 |
U2Xn = 1 |
| UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
| 2400 |
25 |
0.2% |
51 |
0.2% |
47 |
0.0% |
95 |
0.0% |
51 |
0.2% |
103 |
0.2% |
| 4800 |
12 |
0.2% |
25 |
0.2% |
23 |
0.0% |
47 |
0.0% |
25 |
0.2% |
51 |
0.2% |
| 9600 |
6 |
-7.0% |
12 |
0.2% |
11 |
0.0% |
23 |
0.0% |
12 |
0.2% |
25 |
0.2% |
| 14.4k |
3 |
8.5% |
8 |
-3.5% |
7 |
0.0% |
15 |
0.0% |
8 |
-3.5% |
16 |
2.1% |
| 19.2k |
2 |
8.5% |
6 |
-7.0% |
5 |
0.0% |
11 |
0.0% |
6 |
-7.0% |
12 |
0.2% |
| 28.8k |
1 |
8.5% |
3 |
8.5% |
3 |
0.0% |
7 |
0.0% |
3 |
8.5% |
8 |
-3.5% |
| 38.4k |
1 |
-18.6% |
2 |
8.5% |
2 |
0.0% |
5 |
0.0% |
2 |
8.5% |
6 |
-7.0% |
| 57.6k |
0 |
8.5% |
1 |
8.5% |
1 |
0.0% |
3 |
0.0% |
1 |
8.5% |
3 |
8.5% |
| 76.8k |
– |
– |
1 |
-18.6% |
1 |
-25.0% |
2 |
0.0% |
1 |
-18.6% |
2 |
8.5% |
| 115.2k |
– |
– |
0 |
8.5% |
0 |
0.0% |
1 |
0.0% |
0 |
8.5% |
1 |
8.5% |
| 230.4k |
– |
– |
– |
– |
– |
– |
0 |
0.0% |
– |
– |
– |
– |
| 250k |
– |
– |
– |
– |
– |
– |
– |
– |
– |
– |
0 |
0.0% |
| Max.(1) |
62.5 kbps |
125 kbps |
115.2 kbps |
230.4 kbps |
125 kbps |
250 kbps |
Note: 1. UBRRn = 0, Error = 0.0%
Table 2. Examples of UBRRn Settings for
Commonly Used Oscillator Frequencies
| Baud Rate [bps] |
fosc = 3.6864
MHz |
fosc = 4.0000
MHz |
fosc = 7.3728
MHz |
| U2Xn = 0 |
U2Xn = 1 |
U2Xn = 0 |
U2Xn = 1 |
U2Xn = 0 |
U2Xn = 1 |
| UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
| 2400 |
95 |
0.0% |
191 |
0.0% |
103 |
0.2% |
207 |
0.2% |
191 |
0.0% |
383 |
0.0% |
| 4800 |
47 |
0.0% |
95 |
0.0% |
51 |
0.2% |
103 |
0.2% |
95 |
0.0% |
191 |
0.0% |
| 9600 |
23 |
0.0% |
47 |
0.0% |
25 |
0.2% |
51 |
0.2% |
47 |
0.0% |
95 |
0.0% |
| 14.4k |
15 |
0.0% |
31 |
0.0% |
16 |
2.1% |
34 |
-0.8% |
31 |
0.0% |
63 |
0.0% |
| 19.2k |
11 |
0.0% |
23 |
0.0% |
12 |
0.2% |
25 |
0.2% |
23 |
0.0% |
47 |
0.0% |
| 28.8k |
7 |
0.0% |
15 |
0.0% |
8 |
-3.5% |
16 |
2.1% |
15 |
0.0% |
31 |
0.0% |
| 38.4k |
5 |
0.0% |
11 |
0.0% |
6 |
-7.0% |
12 |
0.2% |
11 |
0.0% |
23 |
0.0% |
| 57.6k |
3 |
0.0% |
7 |
0.0% |
3 |
8.5% |
8 |
-3.5% |
7 |
0.0% |
15 |
0.0% |
| 76.8k |
2 |
0.0% |
5 |
0.0% |
2 |
8.5% |
6 |
-7.0% |
5 |
0.0% |
11 |
0.0% |
| 115.2k |
1 |
0.0% |
3 |
0.0% |
1 |
8.5% |
3 |
8.5% |
3 |
0.0% |
7 |
0.0% |
| 230.4k |
0 |
0.0% |
1 |
0.0% |
0 |
8.5% |
1 |
8.5% |
1 |
0.0% |
3 |
0.0% |
| 250k |
0 |
-7.8% |
1 |
-7.8% |
0 |
0.0% |
1 |
0.0% |
1 |
-7.8% |
3 |
-7.8% |
| 0.5M |
– |
– |
0 |
-7.8% |
– |
– |
0 |
0.0% |
0 |
-7.8% |
1 |
-7.8% |
| 1M |
– |
– |
– |
– |
– |
– |
– |
– |
– |
– |
0 |
-7.8% |
| Max.(1) |
230.4 kbps |
460.8 kbps |
250 kbps |
0.5 Mbps |
460.8 kbps |
921.6 kbps |
| (1) UBRRn = 0, Error = 0.0% |
Table 3. Examples of UBRRn Settings for
Commonly Used Oscillator Frequencies
| Baud Rate [bps] |
fosc = 8.0000
MHz |
fosc = 11.0592
MHz |
fosc = 14.7456
MHz |
| U2Xn = 0 |
U2Xn = 1 |
U2Xn = 0 |
U2Xn = 1 |
U2Xn = 0 |
U2Xn = 1 |
| UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
| 2400 |
207 |
0.2% |
416 |
-0.1% |
287 |
0.0% |
575 |
0.0% |
383 |
0.0% |
767 |
0.0% |
| 4800 |
103 |
0.2% |
207 |
0.2% |
143 |
0.0% |
287 |
0.0% |
191 |
0.0% |
383 |
0.0% |
| 9600 |
51 |
0.2% |
103 |
0.2% |
71 |
0.0% |
143 |
0.0% |
95 |
0.0% |
191 |
0.0% |
| 14.4k |
34 |
-0.8% |
68 |
0.6% |
47 |
0.0% |
95 |
0.0% |
63 |
0.0% |
127 |
0.0% |
| 19.2k |
25 |
0.2% |
51 |
0.2% |
35 |
0.0% |
71 |
0.0% |
47 |
0.0% |
95 |
0.0% |
| 28.8k |
16 |
2.1% |
34 |
-0.8% |
23 |
0.0% |
47 |
0.0% |
31 |
0.0% |
63 |
0.0% |
| 38.4k |
12 |
0.2% |
25 |
0.2% |
17 |
0.0% |
35 |
0.0% |
23 |
0.0% |
47 |
0.0% |
| 57.6k |
8 |
-3.5% |
16 |
2.1% |
11 |
0.0% |
23 |
0.0% |
15 |
0.0% |
31 |
0.0% |
| 76.8k |
6 |
-7.0% |
12 |
0.2% |
8 |
0.0% |
17 |
0.0% |
11 |
0.0% |
23 |
0.0% |
| 115.2k |
3 |
8.5% |
8 |
-3.5% |
5 |
0.0% |
11 |
0.0% |
7 |
0.0% |
15 |
0.0% |
| 230.4k |
1 |
8.5% |
3 |
8.5% |
2 |
0.0% |
5 |
0.0% |
3 |
0.0% |
7 |
0.0% |
| 250k |
1 |
0.0% |
3 |
0.0% |
2 |
-7.8% |
5 |
-7.8% |
3 |
-7.8% |
6 |
5.3% |
| 0.5M |
0 |
0.0% |
1 |
0.0% |
– |
– |
2 |
-7.8% |
1 |
-7.8% |
3 |
-7.8% |
| 1M |
– |
– |
0 |
0.0% |
– |
– |
– |
– |
0 |
-7.8% |
1 |
-7.8% |
| Max.(1) |
0.5 Mbps |
1
Mbps |
691.2 kbps |
1.3824 Mbps |
921.6 kbps |
1.8432 Mbps |
| (1) UBRRn = 0, Error = 0.0% |
Table 4. Examples of UBRRn Settings for
Commonly Used Oscillator Frequencies
| Baud Rate
[bps] |
fosc = 16.0000
MHz |
fosc = 18.4320
MHz |
fosc = 20.0000
MHz |
| U2Xn = 0 |
U2Xn =
1 |
U2Xn =
0 |
U2Xn =
1 |
U2Xn
= 0 |
U2Xn
= 1 |
| UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
UBRRn |
Error |
| 2400 |
416 |
-0.1% |
832 |
0.0% |
479 |
0.0% |
959 |
0.0% |
520 |
0.0% |
1041 |
0.0% |
| 4800 |
207 |
0.2% |
416 |
-0.1% |
239 |
0.0% |
479 |
0.0% |
259 |
0.2% |
520 |
0.0% |
| 9600 |
103 |
0.2% |
207 |
0.2% |
119 |
0.0% |
239 |
0.0% |
129 |
0.2% |
259 |
0.2% |
| 14.4k |
68 |
0.6% |
138 |
-0.1% |
79 |
0.0% |
159 |
0.0% |
86 |
-0.2% |
173 |
-0.2% |
| 19.2k |
51 |
0.2% |
103 |
0.2% |
59 |
0.0% |
119 |
0.0% |
64 |
0.2% |
129 |
0.2% |
| 28.8k |
34 |
-0.8% |
68 |
0.6% |
39 |
0.0% |
79 |
0.0% |
42 |
0.9% |
86 |
-0.2% |
| 38.4k |
25 |
0.2% |
51 |
0.2% |
29 |
0.0% |
59 |
0.0% |
32 |
-1.4% |
64 |
0.2% |
| 57.6k |
16 |
2.1% |
34 |
-0.8% |
19 |
0.0% |
39 |
0.0% |
21 |
-1.4% |
42 |
0.9% |
| 76.8k |
12 |
0.2% |
25 |
0.2% |
14 |
0.0% |
29 |
0.0% |
15 |
1.7% |
32 |
-1.4% |
| 115.2k |
8 |
-3.5% |
16 |
2.1% |
9 |
0.0% |
19 |
0.0% |
10 |
-1.4% |
21 |
-1.4% |
| 230.4k |
3 |
8.5% |
8 |
-3.5% |
4 |
0.0% |
9 |
0.0% |
4 |
8.5% |
10 |
-1.4% |
| 250k |
3 |
0.0% |
7 |
0.0% |
4 |
-7.8% |
8 |
2.4% |
4 |
0.0% |
9 |
0.0% |
| 0.5M |
1 |
0.0% |
3 |
0.0% |
– |
– |
4 |
-7.8% |
– |
– |
4 |
0.0% |
| 1M |
0 |
0.0% |
1 |
0.0% |
– |
– |
– |
– |
– |
– |
– |
– |
| Max.(1) |
1
Mbps |
2
Mbps |
1.152 Mbps |
2.304 Mbps |
1.25 Mbps |
2.5 Mbps |
| (1)
UBRRn = 0, Error = 0.0% |