
RM0453 Rev 2
RM0453
Universal synchronous/asynchronous receiver transmitter (USART/UART)
1257
Figure 326. Reception using DMA
Note:
When FIFO management is enabled, the DMA request is triggered by Receive FIFO not
empty (i.e. RXFNE = 1).
Error flagging and interrupt generation in multibuffer communication
If any error occurs during a transaction in multibuffer communication mode, the error flag is
asserted after the current byte. An interrupt is generated if the interrupt enable flag is set.
For framing error, overrun error and noise flag which are asserted with RXNE (RXFNE in
case FIFO mode is enabled) in single byte reception, there is a separate error flag interrupt
enable bit (EIE bit in the USART_CR3 register), which, if set, enables an interrupt after the
current byte if any of these errors occur.
35.5.20 RS232
Hardware
flow
control and RS485 Driver Enable
It is possible to control the serial data flow between 2 devices by using the nCTS input and
the nRTS output. The
shows how to connect 2 devices in this mode:
Figure 327. Hardware flow control between 2 USARTs
TX line
Frame 1
F2
F3
Set by hardware
cleared by DMA read
F1
ai17193c
Frame 2
Frame 3
RXNE flag
USART_RDR
DMA request
DMA reads
USART_RDR
DMA TCIF flag
(transfer complete)
Software configures the
DMA to receive 3 data
blocks and enables
the USART
DMA reads F3
from USART_RDR
The DMA transfer
is complete
(TCIF=1 in
DMA_ISR)
Set by hardware
Cleared
by
software
DMA reads F2
from USART_RDR
DMA reads F1
from USART_RDR
MSv31169V2
TX circuit
USART 1
TX
RX circuit
RX circuit
USART 2
TX circuit
TX
CTS
CTS
RTS
RX
RTS
RX