Oversampling By 16 Or By 8 - ST STM32L4x6 Reference Manual

RM0351
Example 2
To obtain 921.6 Kbaud with f
• 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 193. 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
4 38.4 KBps
5 57.6 KBps
6 115.2 KBps
7 230.4 KBps
8 460.8 KBps
9 921.6 KBps
10 2 MBps
11 3 MBps
12 4MBps
13 5MBps
14 6MBps
15 7MBps
16 9MBps
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.
Universal synchronous asynchronous receiver transmitter (USART)
CK

oversampling by 16 or by 8

Oversampling by 16 (OVER8 = 0)
Actual BRR
2.4 KBps 0x7530
9.6 KBps 0x1D4C
19.2 KBps 0xEA6
38.4 KBps 0x753
57.6 KBps 0x4E2
115.2 KBps 0x271
230.03KBps 0x139
461.54KBps 0x9C
923.08KBps 0x4E
2 MBps 0x24
3 MBps 0x18
4MBps 0x12
N.A N.A
N.A N.A
N.A N.A
N.A N.A
= 48 MHz.
% Error =
(Calculated -
Desired)B.Rate /
Desired B.Rate
0
0
0
0
0
0
0.16
0.16
0.16
0
0
0
N.A
N.A
N.A
N.A
DocID024597 Rev 3
= 72MHz in both cases of
CK
(1)
Oversampling by 8 (OVER8 = 1)
Actual BRR
2.4 KBps 0xEA60
9.6 KBps 0x3A94
19.2 KBps 0x1D46
38.4 KBps 0xEA3
57.6 KBps 0x9C2
115.2 KBps 0x4E1
230.4 KBps 0x270
460.06KBps 0x134
923.07KBps 0x96
2 MBps 0x44
3 MBps 0x30
4MBps 0x22
4965.51KBps 0x16
6MBps 0x14
6857.14KBps 0x12
9MBps 0x10
% Error
0
0
0
0
0
0
0
0.16
0.16
0
0
0
0.69
0
2
0
1195/1693
1282