RM0312 datasheet(233/275 Pages) STMICROELECTRONICS

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RM0312

Universal synchronous/asynchronous receiver transmitter (USART)

249

When a character is received

•

The RXNE bit is set. It indicates that the content of the shift register is transferred to the

RDR.

•

An interrupt is generated if the RIEN bit is set.

•

The error flags can be set if a frame error, noise or an overrun error has been detected

during reception.

•

Clearing the RXNE bit is performed by a software read to the USART_DR register. The

RXNE flag can also be cleared by writing a zero to it. The RXNE bit must be cleared

before the end of the reception of the next character to avoid an overrun error.

Note:

The REN bit should not be reset while receiving data. If the REN bit is disabled during

reception, the reception of the current byte will be aborted.

Break character

When a break character is received, the USART handles it as a framing error.

Idle character

When an idle frame is detected, there is the same procedure as a received data character

plus an interrupt if the ILIEN bit is set.

Overrun error

An overrun error occurs when a character is received when RXNE has not been reset. Data

can not be transferred from the shift register to the RDR register until the RXNE bit is

cleared.

When an overrun error occurs:

•

The OR bit is set.

•

The RDR content will not be lost. The previous data is available when a read to

USART_DR is performed.

•

The shift register will be overwritten. The second data received during overrun is lost.

•

An interrupt is generated if the RIEN bit is set.

•

The OR bit is reset by a read to the USART_SR register followed by a USART_DR

Noise error

Over-sampling techniques are used for data recovery by discriminating between valid

incoming data and noise.

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