The following table contains equations for calculating the baud rate (in bits per second) and for calculating the UBRR value for each mode of operation using an internally generated clock source.
Operating Mode | Equation for Calculating Baud Rate(1) | Equation for Calculating UBRR Value |
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Asynchronous Normal mode (U2X = 0) |
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Asynchronous Double Speed mode (U2X = 1) |
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Synchronous Master mode |
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For standard crystal and resonator frequencies, the most commonly used baud rates for asynchronous operation can be generated by using the UBRR settings as listed in the following table. For details on clock options supported by a device, refer the device datasheet.
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. The error values are calculated using the following equation:
Baud Rate [bps] | fosc = 1.0000MHz | fosc = 1.8432MHz | fosc = 2.0000MHz | |||||||||
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U2X = 0 | U2X = 1 | U2X= 0 | U2X = 1 | U2X = 0 | U2X = 1 | |||||||
UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | 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) | 62.5kbps | 125kbps | 115.2kbps | 230.4kbps | 125kbps | 250kbps | ||||||
Note: 1. UBRR = 0, Error
= 0.0%
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Baud Rate [bps] | fosc = 3.6864MHz | fosc = 4.0000MHz | fosc = 7.3728MHz | |||||||||
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U2X = 0 | U2X = 1 | U2X = 0 | U2X = 1 | U2X = 0 | U2X = 1 | |||||||
UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | 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) | 230.4kbps | 460.8kbps | 250kbps | 0.5Mbps | 460.8kbps | 921.6kbps | ||||||
Note: 1. UBRR = 0, Error
= 0.0%
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Baud Rate [bps] | fosc = 8.0000MHz | fosc = 11.0592MHz | fosc = 14.7456MHz | |||||||||
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U2X = 0 | U2X = 1 | U2X = 0 | U2X = 1 | U2X = 0 | U2X = 1 | |||||||
UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | 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) | 0.5Mbps | 1Mbps | 691.2kbps | 1.3824Mbps | 921.6kbps | 1.8432Mbps | ||||||
Note: 1. UBRR = 0, Error
= 0.0%
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Baud Rate [bps] | fosc = 16.0000MHz | fosc = 18.4320MHz | fosc = 20.0000MHz | |||||||||
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U2X = 0 | U2X = 1 | U2X = 0 | U2X = 1 | U2X = 0 | U2X = 1 | |||||||
UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | Error | UBRR | 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) | 1Mbps | 2Mbps | 1.152Mbps | 2.304Mbps | 1.25Mbps | 2.5Mbps | ||||||
Note: 1. UBRR = 0, Error
= 0.0%
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