DocID024597 Rev 3 1239/1693
RM0351 Universal synchronous asynchronous receiver transmitter (USART)
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Bit 9 CTSIF: CTS interrupt flag
This bit is set by hardware when the CTS input toggles, if the CTSE bit is set. It is cleared by
software, by writing 1 to the CTSCF bit in the USARTx_ICR register.
An interrupt is generated if CTSIE=1 in the USARTx_CR3 register.
0: No change occurred on the CTS status line
1: A change occurred on the CTS status line
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
hardware to ‘0’.
Bit 8 LBDF: LIN break detection flag
This bit is set by hardware when the LIN break is detected. It is cleared by software, by
writing 1 to the LBDCF in the USARTx_ICR.
An interrupt is generated if LBDIE = 1 in the USARTx_CR2 register.
0: LIN Break not detected
1: LIN break detected
Note: If the USART does not support LIN mode, this bit is reserved and forced by hardware
to ‘0’. Please refer to Section 36.4: USART implementation on page 1180.
Bit 7 TXE: Transmit data register empty
This bit is set by hardware when the content of the USARTx_TDR register has been
transferred into the shift register. It is cleared by a write to the USARTx_TDR register.
The TXE flag can also be cleared by writing 1 to the TXFRQ in the USARTx_RQR register,
in order to discard the data (only in smartcard T=0 mode, in case of transmission failure).
An interrupt is generated if the TXEIE bit =1 in the USARTx_CR1 register.
0: data is not transferred to the shift register
1: data is transferred to the shift register)
Note: This bit is used during single buffer transmission.
Bit 6 TC: Transmission complete
This bit is set by hardware if the transmission of a frame containing data is complete and if
TXE is set. An interrupt is generated if TCIE=1 in the USARTx_CR1 register. It is cleared by
software, writing 1 to the TCCF in the USARTx_ICR register or by a write to the
USARTx_TDR register.
An interrupt is generated if TCIE=1 in the USARTx_CR1 register.
0: Transmission is not complete
1: Transmission is complete
Note: If TE bit is reset and no transmission is on going, the TC bit will be set immediately.
Bit 5 RXNE: Read data register not empty
This bit is set by hardware when the content of the RDR shift register has been transferred
to the USARTx_RDR register. It is cleared by a read to the USARTx_RDR register. The
RXNE flag can also be cleared by writing 1 to the RXFRQ in the USARTx_RQR register.
An interrupt is generated if RXNEIE=1 in the USARTx_CR1 register.
0: data is not received
1: Received data is ready to be read.
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