ST STM32F446 Series Reference Manual page 816

Universal synchronous asynchronous receiver transmitter (USART)
Table 155. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
10 921.6 KBps 913.043 KBps
11 1.792 MBps
12 1.8432 MBps
13 3.584 MBps
14 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 156. 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
13 3.584 MBps
14 3.6864 MBps
816/1328
oversampling by 16
Oversampling by 16 (OVER8=0)
f = 42 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
2.875
1.826 MBps 1.4375
1.826 MBps 1.4375
NA NA
NA NA
oversampling by 8
Oversampling by 8 (OVER8=1)
f = 42 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
1.2 KBps NA
2.4 KBps 2187.5
9.6 KBps 546.875
19.195 KBps 273.5
38.391 KBps 136.75
57.613 KBps 91.125
115.068 KBps 45.625
230.769 KBps 22.75
461.538 KBps 11.375
913.043 KBps 5.75
1.826 MBps 2.875
1.826 MBps 2.875
3.5 MBps 1.5
3.82 MBps 1.375
(1)(2)
(continued)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0.93
1.9
0.93
NA
NA
PCLK
(1)(2)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0
0
0
0.02
0.02
0.02
0.11
0.11
0.16
0.93
1.9
0.93
2.34
3.57
RM0390 Rev 4
= 42 MHz or f
PCLK PCLK
f = 84 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
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
= 42 MHz or f
PCLK
f = 84 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
1.2 KBps NA
2.4 KBps NA
9.6 KBps 1093.75
19.2 KBps 546.875
38.391 KBps 273.5
57.613 KBps 182.25
115.226 KBps 91.125
230.137 KBps 45.625
461.538 KBps 22.75
923.076 KBps 11.375
1.787Mbps 5.875
1.826 MBps 5.75
3.652 MBps 2.875
3.652 MBps 2.875
RM0390
= 84 Hz,
%
Error
0.93
0.27
0.93
1.9
0.93
= 84 MHz,
%
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