ST STM32L4+ Series Reference Manual page 1724

Universal synchronous/asynchronous receiver transmitter (USART/UART)
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Figure 490. Word length programming
9-bit word length (M = 01 ), 1 Stop bit
Start
Bit0 Bit1 Bit2
bit
Clock
8-bit word length (M = 00 ), 1 Stop bit
Start
Bit0 Bit1 Bit2
bit
Clock
7-bit word length (M = 10 ), 1 Stop bit
Start
Bit0 Bit1 Bit2
bit
Clock
Data frame
Bit3 Bit4 Bit5 Bit6 Bit7
Idle frame
Break frame
Possible
Data frame Parity
bit
Bit3 Bit4 Bit5 Bit6 Bit7
**
Idle frame
Break frame
Possible
Data frame Parity
bit
Stop
Bit3 Bit4 Bit5 Bit6
bit
**
Idle frame
Break frame
** LBCL bit controls last data clock pulse
RM0432 Rev 6
Possible
Parity
bit
Next
Stop
Start
Bit8
bit
bit
**
Start
bit
Stop Stop
Start
bit bit bit
Next
Stop
Start
bit
bit
Start
bit
Stop Stop
Start
bit bit
bit
Next
Start
bit
Start
bit
Stop Stop Start
bit bit bit
RM0432
MS33194V2