Figure 419. Usart Data Clock Timing Diagram (M Bits = 01); Figure 420. Rx Data Setup/Hold Time - ST STM32L4 5 Series Reference Manual

Universal synchronous asynchronous receiver transmitter (USART)
Note: The function of CK is different in Smartcard mode. Refer to
Smartcard mode
1330/1830

Figure 419. USART data clock timing diagram (M bits = 01)

Figure 420. RX data setup/hold time

for more details.
DocID024597 Rev 5
Section 40.5.13: USART
RM0351