ST STM32F446 Series Reference Manual page 812

Universal synchronous asynchronous receiver transmitter (USART)
Table 150. 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 115.108 KBps
8 230.4 KBps 231.884 KBps
9 460.8 KBps 457.143 KBps
10 921.6 KBps 941.176 KBps
11 2 MBps
12 3 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.
Table 151. 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 19.185 KBps
4 57.6 KBps 57.554 KBps
5 115.2 KBps 115.942 KBps
6 230.4 KBps 228.571 KBps
7 460.8 KBps 470.588 KBps
812/1328
oversampling by 8
Oversampling by 8 (OVER8=1)
f = 16 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
1.2 KBps 1666.625
2.4 KBps 833.375
9.598 KBps 208.375
19.208 KBps 104.125
38.369 KBps 52.125
57.554 KBps 34.75
17.375
8.625
4.375
2.125
2000 KBps 1
NA NA
oversampling by 16
Oversampling by 16 (OVER8=0)
f = 8 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
2.400 KBps 208.3125
9.604 KBps 52.0625
26.0625
8.6875
4.3125
2.1875
1.0625
PCLK
(1)
% Error =
(Calculated -
Desired) B.rate /
Desired B.rate
0
0
0.02
0.04
0.08
0.08
0.08
0.64
0.79
2.12
0
NA
(1)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0.00%
0.04%
0.08%
0.08%
0.64%
0.79%
2.12%
RM0390 Rev 4
= 16 MHz or f
PCLK
f = 24 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
1.2 KBps 2500
2.4 KBps 1250
9.6 KBps 312.5
19.2 KBps 156.25
38.4 KBps 78.125
57.554 KBps 52.125
115.385 KBps 26
230.769 KBps 13
461.538 KBps 6.5
923.077 KBps 3.25
2000 KBps 1.5
3000 KBps 1
= 8 MHz or f
PCLK PCLK
f = 16 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
2.400 KBps 416.6875
9.598 KBps 104.1875
19.208 KBps 52.0625
57.554 KBps 17.3750
115.108 KBps 8.6875
231.884 KBps 4.3125
457.143 KBps 2.1875
RM0390
= 24 MHz,
% Error
0
0
0
0
0
0.08
0.16
0.16
0.16
0.16
0
0
= 16 MHz,
% Error
0.00%
0.02%
0.04%
0.08%
0.08%
0.64%
0.79%