RM0365 Datasheet, PDF (894/1076 Pages) STMicroelectronics – This reference manual targets application developers

RM0365
Universal synchronous asynchronous receiver transmitter (USART)
Bit 22 REACK: Receive enable acknowledge flag
This bit is set/reset by hardware, when the Receive Enable value is taken into account by
the USART.
It can be used to verify that the USART is ready for reception before entering Stop mode.
Note: If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’.
Bit 21 TEACK: Transmit enable acknowledge flag
This bit is set/reset by hardware, when the Transmit Enable value is taken into account by
the USART.
It can be used when an idle frame request is generated by writing TE=0, followed by TE=1
in the USARTx_CR1 register, in order to respect the TE=0 minimum period.
Bit 20 WUF: Wakeup from Stop mode flag
This bit is set by hardware, when a wakeup event is detected. The event is defined by the
WUS bit field. It is cleared by software, writing a 1 to the WUCF in the USARTx_ICR register.
An interrupt is generated if WUFIE=1 in the USARTx_CR3 register.
Note: When UESM is cleared, WUF flag is also cleared.
The WUF interrupt is active only in Stop mode.
If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’.
Bit 19 RWU: Receiver wakeup from Mute mode
This bit indicates if the USART is in mute mode. It is cleared/set by hardware when a
wakeup/mute sequence is recognized. The mute mode control sequence (address or IDLE)
is selected by the WAKE bit in the USARTx_CR1 register.
When wakeup on IDLE mode is selected, this bit can only be set by software, writing 1 to the
MMRQ bit in the USARTx_RQR register.
0: Receiver in active mode
1: Receiver in mute mode
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 USARTx_RQR register. It is automatically reset by hardware
during the stop bit of break transmission.
0: No break character is transmitted
1: Break character will be transmitted
Bit 17 CMF: Character match flag
This bit is set by hardware, when the character defined by ADD[7:0] is received. It is cleared
by software, writing 1 to the CMCF in the USARTx_ICR register.
An interrupt is generated if CMIE=1in the USARTx_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
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