Oversampling By 16 - ST STM32F405 Reference Manual

Universal synchronous asynchronous receiver transmitter (USART)
Table 141. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
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 142. 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
11. 1.792 MBps
12. 1.8432 MBps 1.826 MBps
13. 3.584 MBps
14. 3.6864 MBps N.A
986/1749
oversampling by 8
Oversampling by 8 (OVER8=1)
f = 30 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
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
programmed
Actual
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
1.826 MBps 1.4375
1.4375
N.A N.A
N.A
(1) (2)
(continued)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
1.73%
4.63%
1.73%
NA
NA
(1)(2)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0
0
0
0.02
0.02
0.02
0.11
0.16
0.16
0.93
1.9
0.93
N.A
N.A
RM0090 Rev 18
= 30 MHz or f
PCLK PCLK
f =60 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
1.8182 MBps 4.1250
3.5294 MBps 2.1250
3.7500 MBps 2.0000
7.5000 MBps 1.0000
7.5000 MBps 1.0000
= 42 MHz or f
PCLK PCLK
f = 84 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
1.2 KBps NA
2.4 KBps 2187.5
9.6 KBps 546.875
19.2 KBps 273.4375
38.391 KBps 136.75
57.613 KBps 91.125
115.226 KBps 45.5625
230.137 KBps 22.8125
461.538 KBps 11.375
923.076 KBps 5.6875
1.787 MBps 2.9375
1.826 MBps 2.875
3.652 MBps 1.4375
3.652 MBps 1.4375
RM0090
= 60 MHz,
%
Error
1.36%
1.52%
1.73%
4.63%
1.73%
= 84 Hz,
%
Error
0
0
0
0
0.02
0.02
0.02
0.11
0.16
0.93
0.27
0.93
1.9
0.93