
Universal synchronous/asynchronous receiver transmitter (USART/UART)
RM0453
1196/1454
RM0453 Rev 2
Bit 18
SBKF
: Send break flag
This bit indicates that a send break character was requested. It is set by software, by writing
1 to the SBKRQ bit in the USART_CR3 register. It is automatically reset by hardware during
the stop bit of break transmission.
0: Break character transmitted
1: Break character requested by setting SBKRQ bit in USART_RQR register
Bit 17
CMF
: Character match flag
This bit is set by hardware, when a the character defined by ADD[7:0] is received. It is
cleared by software, writing 1 to the CMCF in the USART_ICR register.
An interrupt is generated if CMIE = 1in the USART_CR1 register.
0: No Character match detected
1: Character Match detected
Bit 16
BUSY
: Busy flag
This bit is set and reset by hardware. It is active when a communication is ongoing on the
RX line (successful start bit detected). It is reset at the end of the reception (successful or
not).
0: USART is idle (no reception)
1: Reception on going
Bit 15
ABRF:
Auto baud rate flag
This bit is set by hardware when the automatic baud rate has been set (RXNE is also set,
generating an interrupt if RXNEIE = 1) or when the auto baud rate operation was completed
without success (ABRE = 1) (ABRE, RXNE and FE are also set in this case)
It is cleared by software, in order to request a new auto baud rate detection, by writing 1 to
the ABRRQ in the USART_RQR register.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and kept
at reset value.
Bit 14
ABRE
: Auto baud rate error
This bit is set by hardware if the baud rate measurement failed (baud rate out of range or
character comparison failed)
It is cleared by software, by writing 1 to the ABRRQ bit in the USART_RQR register.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and kept
at reset value.
Bit 13
UDR
: SPI slave underrun error flag
In slave transmission mode, this flag is set when the first clock pulse for data transmission
appears while the software has not yet loaded any value into USART_TDR. This flag is
reset by setting UDRCF bit in the USART_ICR register.
0: No underrun error
1: underrun error
Note: If the USART does not support the SPI slave mode, this bit is reserved and kept at
reset value. Refer to
Section 35.4: USART implementation on page 1120
Bit 12
EOBF
: End of block flag
This bit is set by hardware when a complete block has been received (for example T = 1
Smartcard mode). The detection is done when the number of received bytes (from the start
of the block, including the prologue) is equal or greater than BLEN + 4.
An interrupt is generated if the EOBIE = 1 in the USART_CR1 register.
It is cleared by software, writing 1 to the EOBCF in the USART_ICR register.
0: End of Block not reached
1: End of Block (number of characters) reached
Note: If Smartcard mode is not supported, this bit is reserved and kept at reset value. Refer