47.7.1.1.1 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.

Table 47-3. Baud Rate Example (OVER = 0)
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%.

Error = 1 Expected Baud Rate Actual Baud Rate