Usart Receiver Tolerance To Clock Deviation - ST STM32F412 Reference Manual

Universal synchronous receiver transmitter (USART) /universal asynchronous receiver transmit-
Table 149. Error calculation for programmed baud rates at f
Baud rate
S.No Desired
1 9.600 KBps
2 19.200 KBps
3 38.400 KBps
4 57.600 KBps
5 115.200 KBps
6 230.400 KBps
7 460.800 KBps
8 921.600 KBps
9 4.000 MBps
10 6.250 MBps
11 12.500 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.
2. Only USART1 and USART6 are clocked with PCLK2. Other USARTs are clocked with PCLK1. Refer to the device
datasheets for the maximum values for PCLK1 and PCLK2.
25.4.5

USART receiver tolerance to clock deviation

The USART asynchronous receiver works correctly only if the total clock system deviation is
smaller than the USART receiver tolerance. The causes that contribute to the total deviation
are:
•
DTRA: Deviation due to the transmitter error (also includes the deviation of the
transmitter local oscillator)
•
DQUANT: Error due to the baud rate quantization of the receiver
• DREC: Deviation of the receiver local oscillator
•
DTCL: Deviation due to the transmission line (generally due to the transceivers that
can introduce an asymmetry between the low-to-high transition timing and the
high-to-low transition timing)
DTRA + DQUANT + DREC + DTCL < USART receiver tolerance
782/1163
oversampling by 8
Oversampling by 8 (OVER8=1)
f = 100 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
9.601 KBps 1302
19.201 KBps 651
38.402 KBps 325.5
57.603 KBps 217
115.207 KBps 108.5
230.414 KBps 54.25
460.829 KBps 27.125
925.925 KBps 13.5
4 MBps 3.125
6.25 MBps 2
12.500 MBps 1
PCLK
(1)(2)
% Error =
(Calculated -
Desired)B.Rate
/Desired B.Rate
0.006
0.006
0.006
0.006
0.006
0.006
0.006
0.470
0.000
0.000
0.000
RM0402 Rev 6
= 100 MHz or f
PCLK
f = 50 MHz
PCLK
Value
programmed
Actual
in the baud
rate register
9.601 KBps 651
19.201 KBps 325.5
38.402 KBps 162.75
57.603 KBps 108.5
115.207 KBps 54.25
230.414 KBps 27.125
462.962 KBps 13.5
925.925 KBps 6.75
4.167 MBps 1.5
6.250 MBps 1
NA NA
= 50 MHz,
%
Error
0.006
0.006
0.006
0.006
0.006
0.006
0.470
0.470
4.170
0.000
NA