ST STM32F446 Series Reference Manual page 814

Universal synchronous asynchronous receiver transmitter (USART)
Table 153. 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 115.385 KBps
6 230.4 KBps 230.769 KBps
7 460.8 KBps 461.538 KBps
8 896 KBps 909.091 KBps
9 921.6 KBps 909.091 KBps
10 1.792 MBps
11 1.8432 MBps
12 3.584 MBps
13 3.6864 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 154. 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
814/1328
oversampling by 16
Oversampling by 16 (OVER8=0)
f = 30 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
2.400 KBps 781.2500
9.600 KBps 195.3125
19.194 KBps 97.6875
57.582KBps 32.5625
16.2500
8.1250
4.0625
2.0625
2.0625
1.1764 MBps 1.0625
1.8750 MBps 1.0000
NA NA
NA NA
oversampling by 8
Oversampling by 8 (OVER8=1)
f = 30 MHz
PCLK
Value
programmed
Actual
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
PCLK
(1)(2)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0.00%
0.00%
0.03%
0.03%
0.16%
0.16%
0.16%
1.46%
1.36%
1.52%
1.73%
NA
NA
PCLK
(1) (2)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0.00%
0.00%
0.03%
0.16%
0.16%
0.16%
RM0390 Rev 4
= 30 MHz or f
PCLK
f = 60 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
2.400 KBps 1562.5000
9.600 KBps 390.6250
19.200 KBps 195.3125
57.582 KBps 65.1250
115.163 KBps 32.5625
230.769 KBps 16.2500
461.538 KBps 8.1250
895.522 KBps 4.1875
923.077 KBps 4.0625
1.8182 MBps 2.0625
1.8182 MBps 2.0625
3.2594 MBps 1.0625
3.7500 MBps 1.0000
= 30 MHz or f
PCLK
f =60 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
2.400 KBps 3125.0000
9.600 KBps 781.2500
19.200 KBps 390.6250
57.582 KBps 130.2500
115.163 KBps 65.1250
230.769 KBps 32.5000
RM0390
= 60 MHz,
%
Error
0.00%
0.00%
0.00%
0.03%
0.03%
0.16%
0.16%
0.05%
0.16%
1.36%
1.52%
1.52%
1.73%
= 60 MHz,
%
Error
0.00%
0.00%
0.00%
0.03%
0.03%
0.16%