Table 146. Noise Detection From Sampled Data; Figure 285. Data Sampling When Oversampling By 8 - ST STM32F446 Series Reference Manual

RM0390
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.
When the framing error is detected:
•
The FE bit is set by hardware
• 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 that 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 FE bit is reset by a USART_SR register read operation followed by a USART_DR
register read operation.
Configurable stop bits during reception
The number of stop bits to be received can be configured through the control bits of Control
Register 2 - it can be either 1 or 2 in normal mode and 0.5 or 1.5 in Smartcard mode.
Universal synchronous asynchronous receiver transmitter (USART)

Figure 285. Data sampling when oversampling by 8

Table 146. Noise detection from sampled data

Sampled value
000
001
010
011
100
101
110
111
NE status
0
1
1
1
1
1
1
0
RM0390 Rev 4
Received bit value
0
0
0
1
0
1
1
1
807/1328
845