DocID018909 Rev 11
973/1731
RM0090
Universal synchronous asynchronous receiver transmitter (USART)
1010
Then, USART_BRR = 0x195 => USARTDIV = 0d25.625
Example 3
:
To program USARTDIV = 0d50.99
This leads to:
DIV_Fraction = 8*0d0.99 = 0d7.92
The nearest real number is 0d8 = 0x8 => overflow of the DIV_frac[2:0] => carry must be
added up to the mantissa
DIV_Mantissa = mantissa (0d50.990 + carry) = 0d51 = 0x33
Then, USART_BRR = 0x0330 => USARTDIV = 0d51.000
Table 133. Error calculation for programmed baud rates at f
PCLK
= 8 MHz or f
PCLK
= 12 MHz,
oversampling by 16
(1)
Oversampling by 16 (OVER8=0)
Baud rate7
f
PCLK
= 8 MHz
f
PCLK
= 12 MHz
S.No
Desired
Actual
Value
programmed
in the baud
rate register
% Error =
(Calculated -
Desired) B.rate /
Desired B.rate
Actual
Value
programmed
in the baud
rate register
% Error
1
1.2 KBps
1.2 KBps
416.6875
0
1.2 KBps
625
0
2
2.4 KBps
2.4 KBps
208.3125
0.01
2.4 KBps
312.5
0
3
9.6 KBps
9.604 KBps
52.0625
0.04
9.6 KBps
78.125
0
4
19.2 KBps
19.185 KBps
26.0625
0.08
19.2 KBps
39.0625
0
5
38.4 KBps
38.462 KBps
13
0.16
38.339 KBps
19.5625
0.16
6
57.6 KBps
57.554 KBps
8.6875
0.08
57.692 KBps
13
0.16
7
115.2 KBps 115.942 KBps
4.3125
0.64
115.385 KBps
6.5
0.16
8
230.4 KBps 228.571 KBps
2.1875
0.79
230.769 KBps
3.25
0.16
9
460.8 KBps 470.588 KBps
1.0625
2.12
461.538 KBps
1.625
0.16
10
921.6 KBps
NA
NA
NA
NA
NA
NA
11
2 MBps
NA
NA
NA
NA
NA
NA
12
3 MBps
NA
NA
NA
NA
NA
NA
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.