DocID13902 Rev 15 806/1128
RM0008 Universal synchronous asynchronous receiver transmitter (USART)
820
1. Write the USART_DR register address in the DMA control register to configure it as the
destination of the transfer. The data will be moved to this address from memory after
each TXE event.
2. Write the memory address in the DMA control register to configure it as the source of
the transfer. The data will be loaded into the USART_DR register from this memory
area after each TXE event.
3. Configure the total number of bytes to be transferred to the DMA control register.
4. Configure the channel priority in the DMA register
5. Configure DMA interrupt generation after half/ full transfer as required by the
application.
6. Clear the TC bit in the SR register by writing 0 to it.
7. Activate the channel in the DMA register.
When the number of data transfers programmed in the DMA Controller is reached, the DMA
controller generates an interrupt on the DMA channel interrupt vector.
In transmission mode, once the DMA has written all the data to be transmitted (the TCIF flag is set in the
DMA_ISR register), the TC flag can be monitored to make sure that the USART communication is
complete. This is required to avoid corrupting the last transmission before disabling the USART or
entering the Stop mode. The software must wait until TC=1. The TC flag remains cleared during all data
transfers and it is set by hardware at the last frame’s end of transmission.
Figure 296. Transmission using DMA
TX line
USART_DR
Frame 1
TXE flag
F2
TC flag
F3
Frame 2
software waits until TC=1
Frame 3
set by hardware
cleared by DMA read
set by hardware
cleared by DMA read
set by hardware
set
Idle preamble
by hardware
F1
software configures
the DMA to send 3
data and enables the
USART
DMA request
ignored by the DMA
DMA writes
flag DMA TCIF
set by hardware
clear
by software
SPI_DR
because DMA transfer is complete
DMA writes F1
into
USART_DR
DMA writes F2
into
USART_DR
DMA writes F3
into
USART_DR.
The DMA transfer
is complete
(TCIF=1 in
DMA_ISR)
(Transfer complete)
ai17192
To Next Page
Loading...
Need help?
General
