ST STM32L4+ Series Reference Manual page 1766

Universal synchronous/asynchronous receiver transmitter (USART/UART)
Figure 514
Figure 514. Wakeup event verified (wakeup event = address match, FIFO disabled)
Usart_ker_ck
Figure 515
Figure 515. Wakeup event not verified (wakeup event = address match,
Usart_ker_ck
Note: The figures above are valid when address match or any received frame is used as wakeup
event. If the wakeup event is the start bit detection, the USART sends the wakeup event to
the MCU at the end of the start bit.
1766/2301
shows the USART behavior when the wakeup event is verified.
Idle
RX line
Startup time
OFF
Low-power mode
shows the USART behavior when the wakeup event is not verified.
Idle
RX line
Startup time
OFF
Address match event WUF ='1'
USART sends a wakeup event to the MCU
Rx data 1
ON
FIFO disabled)
Address does not match
Rx data 1
ON
Low-power mode
RM0432 Rev 6
Data reception goes on
Rx data 2
Run mode
Idle
OFF
RM0432
MSv40856V2
MSv40857V2