ST STM32L4x6 User Manual

Universal synchronous asynchronous receiver transmitter (USART) RM0351
1218/1693 DocID024597 Rev 3
Figure 406. RS232 CTS flow control
Note: For correct behavior, CTS must be asserted at least 3 USART clock source periods before
the end of the current character. In addition it should be noted that the CTSCF flag may not
be set for pulses shorter than 2 x PCLK periods.
RS485 Driver Enable
The driver enable feature is enabled by setting bit DEM in the USARTx_CR3 control
register. This allows the user to activate the external transceiver control, through the DE
(Driver Enable) signal. The assertion time is the time between the activation of the DE signal
and the beginning of the START bit. It is programmed using the DEAT [4:0] bit fields in the
USARTx_CR1 control register. The de-assertion time is the time between the end of the last
stop bit, in a transmitted message, and the de-activation of the DE signal. It is programmed
using the DEDT [4:0] bit fields in the USARTx_CR1 control register. The polarity of the DE
signal can be configured using the DEP bit in the USARTx_CR3 control register.
In USART, the DEAT and DEDT are expressed in sample time units (1/8 or 1/16 bit duration,
depending on the oversampling rate).
36.5.17 Wakeup from Stop mode using USART
The USART is able to wake up the MCU from Stop mode when the UESM bit is set and the
USART clock is set to HSI16 or LSE (refer to Section Reset and clock control (RCC)).
The MCU wakeup from Stop mode can be done using the standard RXNE interrupt. In this
case, the RXNEIE bit must be set before entering Stop mode.
Alternatively, a specific interrupt may be selected through the WUS bit fields.
In order to be able to wake up the MCU from Stop mode, the UESM bit in the USARTx_CR1
control register must be set prior to entering Stop mode.
When the wakeup event is detected, the WUF flag is set by hardware and a wakeup
interrupt is generated if the WUFIE bit is set.
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ST STM32L4x6 Specifications

General

Brand	ST
Model	STM32L4x6
Category	Microcontrollers
Language	English