Oversampling By 8 - STMicroelectronics STM32F405 Reference Manual

Universal synchronous asynchronous receiver transmitter (USART)
Table 139. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
8. 896 KBps
9. 921.6 KBps
10. 1.792 MBps
1.8432
11.
MBps
12. 3.584 MBps
3.6864
13.
MBps
14. 7.168 MBps
7.3728
15.
MBps
1. The lower the CPU clock the lower the accuracy for a particular baud rate. The upper limit of the achievable baud rate can
be fixed with these data.
2. Only USART1 and USART6 are clocked with PCLK2. Other USARTs are clocked with PCLK1. Refer to the device
datasheets for the maximum values for PCLK1 and PCLK2.
Table 140. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
1. 2.4 KBps
2. 9.6 KBps
3. 19.2 KBps
4. 57.6 KBps
5. 115.2 KBps
6. 230.4 KBps
7. 460.8 KBps
8. 896 KBps
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oversampling by 16
Oversampling by 16 (OVER8=0)
f = 30 MHz
PCLK
Value
programme
Actual d in the
baud rate
register
909.091 KBps 2.0625
909.091 KBps 2.0625
1.1764 MBps 1.0625
1.8750 MBps 1.0000
NA NA
NA NA
NA NA
NA NA

oversampling by 8

Oversampling by 8 (OVER8=1)
f = 30 MHz
PCLK
Value
programme
Actual d in the
baud rate
register
2.400 KBps 1562.5000
9.600 KBps 390.6250
19.194 KBps 195.3750
57.582 KBps 65.1250
115.385 KBps 32.5000
230.769 KBps 16.2500
461.538 KBps 8.1250
909.091 KBps 4.1250
DocID018909 Rev 11
PCLK
(1)(2)
(continued)
% Error =
(Calculated -
Actual
Desired)B.Rate
/Desired B.Rate
1.46% 895.522 KBps 4.1875
1.36% 923.077 KBps 4.0625
1.52% 1.8182 MBps
1.73% 1.8182 MBps
NA 3.2594 MBps
NA 3.7500 MBps
NA NA
NA NA
PCLK
(1) (2)
% Error =
(Calculated -
Actual
Desired)B.Rate
/Desired B.Rate
0.00% 2.400 KBps
0.00% 9.600 KBps
0.03% 19.200 KBps
0.16% 57.582 KBps
0.16% 115.163 KBps 65.1250
0.16% 230.769 KBps 32.5000
0.16% 461.538 KBps 16.2500
1.46% 895.522 KBps 8.3750
= 30 MHz or f = 60 MHz,
PCLK
f = 60 MHz
PCLK
Value
programmed
in the baud
rate register
2.0625
2.0625
1.0625
1.0000
NA
NA
= 30 MHz or f = 60 MHz,
PCLK
f =60 MHz
PCLK
Value
programmed
in the baud
rate register
3125.0000
781.2500
390.6250
130.2500
RM0090
%
Error
0.05%
0.16%
1.36%
1.52%
1.52%
1.73%
NA
NA
%
Error
0.00%
0.00%
0.00%
0.03%
0.03%
0.16%
0.16%
0.05%