DocID025202 Rev 7
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RM0365
Universal synchronous asynchronous receiver transmitter (USART)
901
Example 2
To obtain 921.6 Kbaud with f
CK
= 48 MHz.
•
In case of oversampling by 16:
USARTDIV = 48 000 000/921 600
BRR = USARTDIV = 52d = 34h
•
In case of oversampling by 8:
USARTDIV = 2 * 48 000 000/921 600
USARTDIV = 104 (104d = 68h)
BRR[3:0] = USARTDIV[3:0] >> 1 = 8h >> 1 = 4h
BRR = 0x64
Table 154. Error calculation for programmed baud rates at f
CK
= 72MHz in both cases of
oversampling by 16 or by 8
(1)
Baud rate
Oversampling by 16 (OVER8 = 0)
Oversampling by 8 (OVER8 = 1)
S.No
Desired
Actual
BRR
% Error =
(Calculated -
Desired)B.Rate /
Desired B.Rate
Actual
BRR
% Error
1
2.4 KBps
2.4 KBps
0x7530
0
2.4 KBps
0xEA60
0
2
9.6 KBps
9.6 KBps
0x1D4C
0
9.6 KBps
0x3A94
0
3
19.2 KBps
19.2 KBps
0xEA6
0
19.2 KBps
0x1D46
0
4
38.4 KBps
38.4 KBps
0x753
0
38.4 KBps
0xEA3
0
5
57.6 KBps
57.6 KBps
0x4E2
0
57.6 KBps
0x9C2
0
6
115.2 KBps
115.2 KBps
0x271
0
115.2 KBps
0x4E1
0
7
230.4 KBps
230.03KBps
0x139
0.16
230.4 KBps
0x270
0
8
460.8 KBps
461.54KBps
0x9C
0.16
460.06KBps
0x134
0.16
9
921.6 KBps
923.08KBps
0x4E
0.16
923.07KBps
0x96
0.16
10
2 MBps
2 MBps
0x24
0
2 MBps
0x44
0
11
3 MBps
3 MBps
0x18
0
3 MBps
0x30
0
12
4MBps
4MBps
0x12
0
4MBps
0x22
0
13
5MBps
N.A
N.A
N.A
4965.51KBps
0x16
0.69
14
6MBps
N.A
N.A
N.A
6MBps
0x14
0
15
7MBps
N.A
N.A
N.A
6857.14KBps
0x12
2
16
9MBps
N.A
N.A
N.A
9MBps
0x10
0
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.