Datasheet

559
32072H–AVR32–10/2012
AT32UC3A3
This gives a maximum baud rate of CLK_USART divided by 8, assuming that CLK_USART is
the fastest clock available, and that MR.OVER is one.
25.6.4.2 Baud Rate Calculation Example
Table 25-7 shows calculations based on the CD field to obtain 38400 baud from different source
clock frequencies. This table also shows the actual resulting baud rate and error.
The baud rate is calculated with the following formula (MR.OVER=0):
The baud rate error is calculated with the following formula. It is not recommended to work with
an error higher than 5%.
25.6.4.3 Fractional Baud Rate in Asynchronous Mode
The baud rate generator has a limitation: the source frequency is always a multiple of the baud
rate. An approach to this problem is to integrate a high resolution fractional N clock generator,
outputting fractional multiples of the reference source clock. This fractional part is selected with
Table 25-7. Baud Rate Example (OVER=0)
Source Clock (Hz)
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%
60 000 000 38 400 97.66 98 38 265.31 0.35%
BaudRate
CLK_USART
CD 16⋅
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Error 1
ExpectedBaudRate
ActualBaudRate
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