Figure 394. Usart Example Of Synchronous Transmission; Figure 395. Usart Data Clock Timing Diagram (M Bits = 00) - ST STM32L4x6 Reference Manual

RM0351 Universal synchronous asynchronous receiver transmitter (USART)
written). This means that it is not possible to receive synchronous data without transmitting
data.
The LBCL, CPOL and CPHA bits have to be selected when the USART is disabled (UE=0)
to ensure that the clock pulses function correctly.

Figure 394. USART example of synchronous transmission

Figure 395. USART data clock timing diagram (M bits = 00)

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