Figure 326. Usart Example Of Synchronous Transmission; Figure 327. Usart Data Clock Timing Diagram (M Bits = 00) - STMicroelectronics RM0365 Reference Manual

RM0365
Note: The CK pin works in conjunction with the TX pin. Thus, the clock is provided only if the
transmitter is enabled (TE=1) and data is being transmitted (the data register USART_TDR
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.
Universal synchronous asynchronous receiver transmitter (USART)

Figure 326. USART example of synchronous transmission

Figure 327. USART data clock timing diagram (M bits = 00)

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