Low-power universal asynchronous receiver transmitter (LPUART) RM0367
840/1043 RM0367 Rev 7
Character reception
During an LPUART reception, data shifts in least significant bit first (default configuration)
through the RX pin. In this mode, the LPUART_RDR register consists of a buffer (RDR)
between the internal bus and the received shift register.
Character reception procedure
1. Program the M bits in LPUART_CR1 to define the word length.
2. Select the desired baud rate using the baud rate register LPUART_BRR
3. Program the number of stop bits in LPUART_CR2.
4. Enable the LPUART by writing the UE bit in LPUART_CR1 register to 1.
5. Select DMA enable (DMAR) in LPUART_CR3 if multibuffer communication is to take
place. Configure the DMA register as explained in multibuffer communication.
6. Set the RE bit LPUART_CR1. This enables the receiver which begins searching for a
start bit.
When a character is received
• The RXNE bit is set. It indicates that the content of the shift register is transferred to the
RDR. In other words, data has been received and can be read (as well as its
associated error flags).
• An interrupt is generated if the RXNEIE bit is set.
• The error flags can be set if a frame error, noise or an overrun error has been detected
during reception. PE flag can also be set with RXNE.
• In multibuffer, RXNE is set after every byte received and is cleared by the DMA read of
the Receive data Register.
• In single buffer mode, clearing the RXNE bit is performed by a software read to the
LPUART_RDR register. The RXNE flag can also be cleared by writing 1 to the RXFRQ
in the LPUART_RQR register. The RXNE bit must be cleared before the end of the
reception of the next character to avoid an overrun error.
Break character
When a break character is received, the LPUART handles it as a framing error.
Idle character
When an idle frame is detected, there is the same procedure as for a received data
character plus an interrupt if the IDLEIE bit is set.
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