Oversampling By 16 - STMicroelectronics STM32F405 Reference Manual

RM0090
Table 140. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
9. 921.6 KBps
10. 1.792 MBps
11. 1.8432 MBps
12. 3.584 MBps
13. 3.6864 MBps
14. 7.168 MBps
15. 7.3728 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 141. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
1 1.2 KBps
2 2.4 KBps
3 9.6 KBps
4 19.2 KBps
5 38.4 KBps
6 57.6 KBps
7 115.2 KBps
8 230.4 KBps
9 460.8 KBps
10 921.6 KBps
Universal synchronous asynchronous receiver transmitter (USART)
oversampling by 8
Oversampling by 8 (OVER8=1)
f = 30 MHz
PCLK
Value
programme
Actual d in the
baud rate
register
909.091 KBps 4.1250
1.7647 MBps 2.1250
1.8750 MBps 2.0000
3.7500 MBps 1.0000
3.7500 MBps 1.0000
NA NA
NA NA

oversampling by 16

Oversampling by 16 (OVER8=0)
f = 42 MHz
PCLK
Value
programme
Actual d in the
baud rate
register
1.2 KBps 2187.5
2.4 KBps 1093.75
9.6 KBps 273.4375
19.195 KBps 136.75
38.391 KBps 68.375
57.613 KBps 45.5625
115.068 KBps 22.8125
230.769 KBps 11.375
461.538 KBps 5.6875
913.043 KBps 2.875
DocID018909 Rev 11
= 30 MHz or f
PCLK
(1) (2)
(continued)
% Error =
(Calculated -
Actual
Desired)B.Rate
/Desired B.Rate
1.36% 923.077 KBps 8.1250
1.52% 1.8182 MBps
1.73% 1.8182 MBps
4.63% 3.5294 MBps
1.73% 3.7500 MBps
NA 7.5000 MBps
NA 7.5000 MBps
PCLK
(1)(2)
% Error =
(Calculated -
Actual
Desired)B.Rate
/Desired B.Rate
0 1.2 KBps
0 2.4 KBps
0 9.6 KBps
0.02 19.2 KBps
0.02 38.391 KBps
0.02 57.613 KBps
0.11 115.226 KBps
0.16 230.137 KBps
0.16 461.538 KBps
0.93 923.076 KBps
= 60 MHz,
PCLK
f =60 MHz
PCLK
Value
programmed
in the baud
rate register
4.1250
4.1250
2.1250
2.0000
1.0000
1.0000
= 42 MHz or f = 84 Hz,
PCLK
f = 84 MHz
PCLK
Value
programmed
in the baud
rate register
4375
2187.5
546.875
273.4375
136.75
91.125
45.5625
22.8125
11.375
5.6875
%
Error
0.16%
1.46%
1.36%
1.52%
1.73%
4.63%
1.73%
%
Error
0
0
0
0
0.02
0.02
0.02
0.11
0.16
0.93
979/1731
1010