ST STM32WL5 Series Reference Manual page 1181

RM0453
Bit 4 IDLEIE: IDLE interrupt enable
This bit is set and cleared by software.
0: Interrupt inhibited
1: USART interrupt generated whenever IDLE = 1 in the USART_ISR register
Bit 3 TE: Transmitter enable
This bit enables the transmitter. It is set and cleared by software.
0: Transmitter is disabled
1: Transmitter is enabled
Note: During transmission, a low pulse on the TE bit ('0' followed by '1') sends a preamble
Bit 2 RE: Receiver enable
This bit enables the receiver. It is set and cleared by software.
0: Receiver is disabled
1: Receiver is enabled and begins searching for a start bit
Bit 1 UESM: USART enable in low-power mode
When this bit is cleared, the USART cannot wake up the MCU from low-power mode.
When this bit is set, the USART can wake up the MCU from low-power mode.
This bit is set and cleared by software.
0: USART not able to wake up the MCU from low-power mode.
1: USART able to wake up the MCU from low-power mode.
Note: It is recommended to set the UESM bit just before entering low-power mode and clear it
Bit 0 UE: USART enable
When this bit is cleared, the USART prescalers and outputs are stopped immediately, and all
current operations are discarded. The USART configuration is kept, but all the USART_ISR
status flags are reset. This bit is set and cleared by software.
0: USART prescaler and outputs disabled, low-power mode
1: USART enabled
Note: To enter low-power mode without generating errors on the line, the TE bit must be
Universal synchronous/asynchronous receiver transmitter (USART/UART)
(idle line) after the current word, except in Smartcard mode. In order to generate an idle
character, the TE must not be immediately written to '1'. To ensure the required duration,
the software can poll the TEACK bit in the USART_ISR register.
In Smartcard mode, when TE is set, there is a 1 bit-time delay before the transmission
starts.
when exit from low-power mode.
If the USART does not support the wakeup from Stop feature, this bit is reserved and
must be kept at reset value. Refer to
page 1129.
previously reset and the software must wait for the TC bit in the USART_ISR to be set
before resetting the UE bit.
The DMA requests are also reset when UE = 0 so the DMA channel must be disabled
before resetting the UE bit.
In Smartcard mode, (SCEN = 1), the SCLK is always available when CLKEN = 1,
regardless of the UE bit value.
RM0453 Rev 1
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