DocID13902 Rev 15 790/1128
RM0008 Universal synchronous asynchronous receiver transmitter (USART)
820
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.
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 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 FE bit is reset by a USART_SR register read operation followed by a USART_DR
register read operation.
Table 191. Noise detection from sampled data
Sampled value NE status Received bit value Data validity
000 0 0 Valid
001 1 0 Not Valid
010 1 0 Not Valid
011 1 1 Not Valid
100 1 0 Not Valid
101 1 1 Not Valid
110 1 1 Not Valid
111 0 1 Valid
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