at91sam9263 ATMEL Corporation, at91sam9263 Datasheet - Page 513

• Manufacturer Part Number: at91sam9263
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

Table 33-2.
33.6.1.3
6249D–ATARM–20-Dec-07
Source Clock
14 318 180
14 745 600
18 432 000
24 000 000
24 576 000
25 000 000
32 000 000
32 768 000
33 000 000
40 000 000
50 000 000
60 000 000
70 000 000
Fractional Baud Rate in Asynchronous Mode
Baud Rate Example (OVER = 0) (Continued)
Expected Baud
The baud rate is calculated with the following formula:
The baud rate error is calculated with the following formula. It is not recommended to work with
an error higher than 5%.
The Baud Rate generator previously defined is subject to the following limitation: the output fre-
quency changes by only integer multiples of the reference frequency. An approach to this
problem is to integrate a fractional N clock generator that has a high resolution. The generator
architecture is modified to obtain Baud Rate changes by a fraction of the reference source clock.
This fractional part is programmed with the FP field in the Baud Rate Generator Register
(US_BRGR). If FP is not 0, the fractional part is activated. The resolution is one eighth of the
clock divider. This feature is only available when using USART normal mode. The fractional
Baud Rate is calculated using the following formula:
The modified architecture is presented below:
Baudrate
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
Rate
BaudRate
Error
=
=
---------------------------------------------------------------- -
⎛
⎝
1
8 2 Over
–
Calculation Result
(
=
⎛
⎝
ExpectedBaudRate
-------------------------------------------------- -
SelectedClock
–
MCK CD
ActualBaudRate
113.93
23.30
24.00
30.00
39.06
40.00
40.69
52.08
53.33
53.71
65.10
81.38
97.66
) CD
⁄
⎛
⎝
×
+
16
FP
------ -
8
⎞
⎠
⎞
⎠
⎞
⎠
114
CD
23
24
30
39
40
40
52
53
54
65
81
98
AT91SAM9263 Preliminary
Actual Baud Rate
38 908.10
38 400.00
38 400.00
38 461.54
38 400.00
38 109.76
38 461.54
38 641.51
38 194.44
38 461.54
38 580.25
38 265.31
38 377.19
1.31%
0.00%
0.00%
0.16%
0.00%
0.76%
0.16%
0.63%
0.54%
0.16%
0.47%
0.35%
0.06%
Error
513