RM0312 datasheet(234/275 Pages) STMICROELECTRONICS

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Universal synchronous/asynchronous receiver transmitter (USART)

RM0312

234/275

DocID022352 Rev 3

Figure 86. Data sampling for noise detection

Note:

The sample clock frequency is 16x baud rate.

When noise is detected in a frame:

•

The NF is set at the rising edge of the RXNE bit.

•

The invalid data is transferred from the Shift register to the USART_DR register.

This bit rises at the same time as the RXNE bit which generates an interrupt. The NF 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.

The FE bit is reset by a USART_SR register read operation followed by a USART_DR

RX LINE

Sample

clock

12345678910

11 12

sampled values

One bit time

6/16

7/16

Table 45. Noise detection from sampled data

Sampled value

NF status

Received bit value

Data validity

000

Valid

001

Not Valid

010

Not Valid

011

Not Valid

100

Not Valid

101

Not Valid

110

Not Valid

111

Valid

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