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                                样例使用说明
                             Sample Description
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功能描述：
此样例是利用DMA对串口外设接口（SPI）与外部设备以全双工串行方式进行通信的演示,此
接口设置为主模式，为外部从设备提供通信时钟SCK。主机通过MOSI引脚发送数据,从MISO
引脚接收从机的数据，数据以主机提供的SCK沿同步被移位，完成全双工通信。

Function descriptions:
This sample demonstrates communication with an external device in full-duplex 
serial mode using DMA for the SPI peripheral interface. The interface is set 
to master mode, providing the communication clock SCK to the external slave 
device. The master sends data through the MOSI pin and receives data from the 
slave through the MISO pin. The data is shifted along the provided SCK edge, 
enabling full-duplex communication.
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测试环境：
测试用板：PY32M030_STK
MDK版本： 5.28
IAR版本： 9.20
GCC版本： GNU Arm Embedded Toolchain 10.3-2021.10

Test environment:
Test board: PY32M030_STK
MDK Version: 5.28
IAR Version: 9.20
GCC Version: GNU Arm Embedded Toolchain 10.3-2021.10
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使用步骤:
1.选择两块PY32M030_STK板，一块作为主机，一块作为从机；
2.编译下载主机程序（本样例程序）；
3.编译下载从机程序SPI_TwoBoards_FullDuplexSlave_DMA_Init；
4.主机与从机引脚连接(箭头指向为信号传输方向) 
主机MASTER：         从机SLAVE：
SCK(PB3)   ----->    SCK(PB3)
MISO(PB4)  <-----    MISO(PB4)
MOSI(PB5)  ----->    MOSI(PB5)
GND       <----->   GND
5.主从机上电；
6.按下从机复位按键先运行从机程序，再按下主机用户按键运行主机程序；
7.观察到主从机绿灯都保持“常亮”则通信成功，否则“闪烁”通信失败。

Example execution steps:
1.Select two PY32M030_STK boards, one as the master and one as the slave.
2.Compile and download the master program (this sample program).
3.Compile and download the slave program 
"SPI_TwoBoards_FullDuplexSlave_DMA_Init".
4.Connect the pins between the master and slave (direction indicated by 
the arrow):
Master: Slave:
SCK(PB3) -----> SCK(PB3)
MISO(PB4) <----- MISO(PB4)
MOSI(PB5) -----> MOSI(PB5)
GND <-----> GND
5.Power on the master and slave.
6.Press the reset button on the slave first to run the slave program, 
then press the user button on the master to run the master program.
7.If both the master and slave LEDs remain constantly on, the communication 
is successful. If they blink, it indicates communication failure.
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注意事项:
1.必须先按从机复位按键使从机程序先运行，再按主机用户按键开始运行主机程序，否则会
导致主从机通信失败。
2.主机模式可通过程序设置IO控制方式为DMA方式、中断方式和查询方式
3.NSS引脚只需要在使用NSS硬件方式时连接（本样例使用的是NSS软件方式，无需连接NSS引
脚）

Notes:
1.It is necessary to press the reset button on the slave first to run the 
slave program, and then press the user button on the master to start running 
the master program, otherwise it will result in communication failure between 
the master and slave.
2.The master mode can be configured through the program to control IO using 
DMA, interrupt, or polling modes.
3.The NSS pin only needs to be connected when using NSS hardware mode (this 
sample uses NSS software mode, so the NSS pin does not need to be connected).
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