57.7.1.1.1 Baud Rate Calculation Example
The following table shows calculations of CD to obtain a baud rate at 38,400 bit/s for different source clock frequencies. It also shows the actual resulting baud rate and the error.
| Source Clock (MHz) |
Expected Baud Rate (bit/s) |
Calculation Result | CD | Actual Baud Rate (bit/s) |
Error |
|---|---|---|---|---|---|
| 3,686,400 | 38,400 | 6.00 | 6 | 38,400.00 | 0.00% |
| 4,915,200 | 38,400 | 8.00 | 8 | 38,400.00 | 0.00% |
| 5,000,000 | 38,400 | 8.14 | 8 | 39,062.50 | 1.70% |
| 7,372,800 | 38,400 | 12.00 | 12 | 38,400.00 | 0.00% |
| 8,000,000 | 38,400 | 13.02 | 13 | 38,461.54 | 0.16% |
| 12,000,000 | 38,400 | 19.53 | 20 | 37,500.00 | 2.40% |
| 12,288,000 | 38,400 | 20.00 | 20 | 38,400.00 | 0.00% |
| 14,318,180 | 38,400 | 23.30 | 23 | 38,908.10 | 1.31% |
| 14,745,600 | 38,400 | 24.00 | 24 | 38,400.00 | 0.00% |
| 18,432,000 | 38,400 | 30.00 | 30 | 38,400.00 | 0.00% |
| 24,000,000 | 38,400 | 39.06 | 39 | 38,461.54 | 0.16% |
| 24,576,000 | 38,400 | 40.00 | 40 | 38,400.00 | 0.00% |
| 25,000,000 | 38,400 | 40.69 | 40 | 38,109.76 | 0.76% |
| 32,000,000 | 38,400 | 52.08 | 52 | 38,461.54 | 0.16% |
| 32,768,000 | 38,400 | 53.33 | 53 | 38,641.51 | 0.63% |
| 33,000,000 | 38,400 | 53.71 | 54 | 38,194.44 | 0.54% |
| 40,000,000 | 38,400 | 65.10 | 65 | 38,461.54 | 0.16% |
| 50,000,000 | 38,400 | 81.38 | 81 | 38,580.25 | 0.47% |
The baud rate is calculated with the following formula:
Baud rate = MCK / CD × 16
The baud rate error is calculated with the following formula. It is not recommended to work with an error higher than 5%.