RM0453 Rev 2 1179/1454
RM0453 Universal synchronous/asynchronous receiver transmitter (USART/UART)
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Bit 11 CLKEN: Clock enable
This bit enables the user to enable the CK pin.
0: CK pin disabled
1: CK pin enabled
This bit can only be written when the USART is disabled (UE = 0).
Note: If neither synchronous mode nor Smartcard mode is supported, this bit is reserved and must
be kept at reset value. Refer to Section 35.4: USART implementation on page 1120.
In Smartcard mode, in order to provide correctly the CK clock to the smartcard, the steps
below must be respected:
UE = 0
SCEN = 1
GTPR configuration
CLKEN= 1
UE = 1
Bit 10 CPOL: Clock polarity
This bit enables the user to select the polarity of the clock output on the CK pin in synchronous
mode. It works in conjunction with the CPHA bit to produce the desired clock/data relationship
0: Steady low value on CK pin outside transmission window
1: Steady high value on CK pin outside transmission window
This bit can only be written when the USART is disabled (UE = 0).
Note: If synchronous mode is not supported, this bit is reserved and must be kept at reset value.
Refer to Section 35.4: USART implementation on page 1120.
Bit 9 CPHA: Clock phase
This bit is used to select the phase of the clock output on the CK pin in synchronous mode. It works
in conjunction with the CPOL bit to produce the desired clock/data relationship (see Figure 311 and
Figure 312)
0: The first clock transition is the first data capture edge
1: The second clock transition is the first data capture edge
This bit can only be written when the USART is disabled (UE = 0).
Note: If synchronous mode is not supported, this bit is reserved and must be kept at reset value.
Refer to Section 35.4: USART implementation on page 1120.
Bit 8 LBCL: Last bit clock pulse
This bit is used to select whether the clock pulse associated with the last data bit transmitted (MSB)
has to be output on the CK pin in synchronous mode.
0: The clock pulse of the last data bit is not output to the CK pin
1: The clock pulse of the last data bit is output to the CK pin
Caution: The last bit is the 7th or 8th or 9th data bit transmitted depending on the 7 or 8 or 9 bit
format selected by the M bit in the USART_CR1 register.
This bit can only be written when the USART is disabled (UE = 0).
Note: If synchronous mode is not supported, this bit is reserved and must be kept at reset value.
Refer to Section 35.4: USART implementation on page 1120.
Bit 7 Reserved, must be kept at reset value.
Bit 6 LBDIE: LIN break detection interrupt enable
Break interrupt mask (break detection using break delimiter).
0: Interrupt is inhibited
1: An interrupt is generated whenever LBDF = 1 in the USART_ISR register
Note: If LIN mode is not supported, this bit is reserved and must be kept at reset value. Refer to
Section 35.4: USART implementation on page 1120.
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