AN3117 datasheet(21/28 Pages) STMICROELECTRONICS

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AN3117

DMA programming examples

Doc ID 16846 Rev 4

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4.4

DMA transfer examples in low power mode

4.4.1

DMA transfer example in Wait for event (WFE) mode

This example uses the DMA peripheral in circular mode to transfer data from the USARTx

peripheral to the RAM memory. When the user sends a character using USARTx, it is

transferred to a specific RAM buffer using the DMA.

Figure 6.

DMA transfer example in WFE mode

The DMA event is provided by the USARTx_RX.

After configuring USART DMA Channel RX to transfer 4 bytes of data from the USARTx

data register to a RAM buffer, the MCU enters WFE mode.

As long as no “DMA transfer complete” event has occurred, the MCU is in WFE mode. As

soon as the “DMA transfer complete” event occurs, the MCU returns to Run mode and

executes a specific action (activate/deactivate LEDs) depending on the data in the RAM

buffer. The MCU is then returned to WFE mode by software. Since USART DMA Channel

RX is configured in circular mode, the same procedure is repeated indefinitely.

The code for this example is provided in the STM8L05x/STM8L15x/STM8L16x/STM8AL31x/

STM8AL3Lx standard peripheral library package.

Note:

USART DMA Channel RX can be DMA channel 2 or DMA channel 3 respectively for

USART1 and USART2.

GPIO

STM8 core

USARTx

Channel RX

DMA

source

System

bus

DMA1 bus

ai17421c

char 01

char 02

char 03

char 04

DMA

destination

USART DMA1

USARTx_DR

RAM bus

LEDs

Peripheral bus

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