Table 66. Noise Detection From Sampled Data; Figure 168. Data Sampling For Noise Detection - ST STM32F101 Series Reference Manual

RM0008
when the new data is received during the reading sequence (between the USART_SR
register read access and the USART_DR read access).
Noise error
Over-sampling techniques are used (except in synchronous mode) for data recovery by
discriminating between valid incoming data and noise.

Figure 168. Data sampling for noise detection

RX LINE
Sample
clock
Table 66.
Sampled value
When noise is detected in a frame:
The NE is set at the rising edge of the RXNE bit.
The invalid data is transferred from the Shift register to the USART_DR register.
No interrupt is generated in case of single byte communication. However this bit rises
at the same time as the RXNE bit which itself generates an interrupt. In case of
multibuffer communication an interrupt will be issued if the EIE bit is set in the
USART_CR3 register.
The NE bit is reset by a USART_SR register read operation followed by a USART_DR
register read operation.
Framing error
A framing error is detected when:
The stop bit is not recognized on reception at the expected time, following either a de-
synchronization or excessive noise.
Universal synchronous asynchronous receiver transmitter (USART)
1 2 3 4
7/16
Noise detection from sampled data
NE status
000
001
010
011
100
101
110
111
sampled values
5 6 7 8 9 10
One bit time
Received bit value
0
1
1
1
1
1
1
0
11 12 13 14 15 16
6/16
7/16
Data validity
0 Valid
0 Not Valid
0 Not Valid
1 Not Valid
0 Not Valid
1 Not Valid
1 Not Valid
1 Valid
439/501