ST STM32L4x6 Reference Manual page 1230

Universal synchronous asynchronous receiver transmitter (USART)
Bits 21:20 WUS[1:0]: Wakeup from Stop mode interrupt flag selection
Note: If the USART does not support the wakeup from Stop feature, this bit is reserved and
Bits 19:17 SCARCNT[2:0]: Smartcard auto-retry count
Note: If Smartcard mode is not supported, this bit is reserved and forced by hardware to '0'.
Bit 16 Reserved, must be kept at reset value.
Bit 15 DEP: Driver enable polarity selection
Note: If the Driver Enable feature is not supported, this bit is reserved and must be kept
Bit 14 DEM: Driver enable mode
Note: If the Driver Enable feature is not supported, this bit is reserved and must be kept
Bit 13 DDRE: DMA Disable on Reception Error
Note: The reception errors are: parity error, framing error or noise error.
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This bit-field specify the event which activates the WUF (wakeup from Stop mode flag).
00: WUF active on address match (as defined by ADD[7:0] and ADDM7)
01:Reserved.
10: WuF active on Start bit detection
11: WUF active on RXNE.
This bit field can only be written when the USART is disabled (UE=0).
forced by hardware to '0'.
This bit-field specifies the number of retries in transmit and receive, in Smartcard mode.
In transmission mode, it specifies the number of automatic retransmission retries, before
generating a transmission error (FE bit set).
In reception mode, it specifies the number or erroneous reception trials, before generating a
reception error (RXNE and PE bits set).
This bit field must be programmed only when the USART is disabled (UE=0).
When the USART is enabled (UE=1), this bit field may only be written to 0x0, in order to stop
retransmission.
0x0: retransmission disabled - No automatic retransmission in transmit mode.
0x1 to 0x7: number of automatic retransmission attempts (before signaling error)
Please refer to Section 36.4: USART implementation on page
0: DE signal is active high.
1: DE signal is active low.
This bit can only be written when the USART is disabled (UE=0).
cleared. Please refer to
This bit allows the user to activate the external transceiver control, through the DE signal.
0: DE function is disabled.
1: DE function is enabled. The DE signal is output on the RTS pin.
This bit can only be written when the USART is disabled (UE=0).
cleared. Section 36.4: USART implementation on page
0: DMA is not disabled in case of reception error. The corresponding error flag is set but
RXNE is kept 0 preventing from overrun. As a consequence, the DMA request is not
asserted, so the erroneous data is not transferred (no DMA request), but next correct
received data will be transferred (used for Smartcard mode).
1: DMA is disabled following a reception error. The corresponding error flag is set, as well as
RXNE. The DMA request is masked until the error flag is cleared. This means that the
software must first disable the DMA request (DMAR = 0) or clear RXNE before clearing the
error flag.
This bit can only be written when the USART is disabled (UE=0).
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Section 36.4: USART implementation on page
RM0351
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