Universal synchronous asynchronous receiver transmitter (USART) RM0090
974/1731 DocID018909 Rev 11
Table 134. Error calculation for programmed baud rates at f
PCLK
= 8 MHz or f
PCLK
=12 MHz,
oversampling by 8
(1)
Oversampling by 8 (OVER8 = 1)
Baud rate 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 833.375 0 1.2 KBps 1250 0
2 2.4 KBps 2.4 KBps 416.625 0.01 2.4 KBps 625 0
3 9.6 KBps 9.604 KBps 104.125 0.04 9.6 KBps 156.25 0
4 19.2 KBps 19.185 KBps 52.125 0.08 19.2 KBps 78.125 0
5 38.4 KBps 38.462 KBps 26 0.16 38.339 KBps 39.125 0.16
6 57.6 KBps 57.554 KBps 17.375 0.08 57.692 KBps 26 0.16
7 115.2 KBps 115.942 KBps 8.625 0.64 115.385 KBps 13 0.16
8 230.4 KBps 228.571 KBps 4.375 0.79 230.769 KBps 6.5 0.16
9 460.8 KBps 470.588 KBps 2.125 2.12 461.538 KBps 3.25 0.16
10 921.6 KBps 888.889 KBps 1.125 3.55 923.077 KBps 1.625 0.16
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.
Table 135. Error calculation for programmed baud rates at f
PCLK
= 16 MHz or f
PCLK
= 24 MHz,
oversampling by 16
(1)
Oversampling by 16 (OVER8 = 0)
Baud rate
f
PCLK
= 16 MHz f
PCLK
= 24 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 833.3125 0 1.2 1250 0
2 2.4 KBps 2.4 KBps 416.6875 0 2.4 625 0
3 9.6 KBps 9.598 KBps 104.1875 0.02 9.6 156.25 0
4 19.2 KBps 19.208 KBps 52.0625 0.04 19.2 78.125 0
5 38.4 KBps 38.369 KBps 26.0625 0.08 38.4 39.0625 0
6 57.6 KBps 57.554 KBps 17.375 0.08 57.554 26.0625 0.08
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