RM0402 Rev 6 771/1163
RM0402 Universal synchronous receiver transmitter (USART) /universal asynchronous receiver
810
Figure 251. Data sampling when oversampling by 8
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.
Table 137. Noise detection from sampled data
Sampled value NE status Received bit value
000 0 0
001 1 0
010 1 0
011 1 1
100 1 0
101 1 1
110 1 1
111 0 1
MSv31153V1
1 2 3 4 5 6 7
sampled values
2/8
3/8
3/8
One bit time
Sample
clock (x8)
RX line
8
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