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                                样例使用说明
                                Sample Description
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功能描述:
此样例是通过轮询方式对串口外设接口（SPI）与外部设备以全双工串行方式进行通信的演
示。主设备提供通信时钟SCK，通过MOSI/MISO引脚发送/接收数据。从设备通过MOSI/MISO引
脚接收/发送数据。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 is a demonstration of the Serial Peripheral Interface (SPI) 
communicating with an external device in full-duplex serial mode by polling. 
The master device provides the communication clock SCK and sends/receives data 
via the MOSI/MISO pin. The slave device receives/transmits data through the 
MOSI/MISO pins. The data is shifted synchronously along the SCK provided by the 
master to complete full-duplex communication.

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测试环境：
测试用板：PY32L020_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: PY32L020_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PY32L020_STK板，一块作为主机，一块作为从机
2.编译下载主机程序SPI_TwoBoards_FullDuplexMaster_Polling_Init
3.编译下载从机程序SPI_TwoBoards_FullDuplexSlave_Polling_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(PB2)   ----->    SCK(PB2)
MISO(PA1)  <-----    MISO(PA1)
MOSI(PA7)  ----->    MOSI(PA7)
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.观察串口助手，如果主、从机串口助手均接收到“SPI transfer succeeded”则通信成功；
如果主、从机串口助手接收到“SPI Transfer Error”则通信失败。

Example execution steps:
1.Select two PY32L020_STK boards, one as the host and one as the slave
2.Compile and download the host program SPI_TwoBoards_FullDuplexMaster_Polling
_Init
3.Compile and download the slave program SPI_TwoBoards_FullDuplexSlave_Polling
_Init
4.Connect the host and slave pins as follows (the arrows point to indicate the
direction of signal transmission)
MASTER：             SLAVE：
SCK(PB2)   ----->    SCK(PB2)
MISO(PA1)  <-----    MISO(PA1)
MOSI(PA7)  ----->    MOSI(PA7)
GND       <----->    GND
5.Power on the master and slave
6.Press the slave reset button to run the slave program first, then press the
host user button to run the host program
7.Observe the serial assistant, if both master and slave serial assistant 
receive"SPI transfer succeeded", the communication is successful;
If the master and slave serial assistant receive "SPI Transfer Error",the
communication fails.
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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）
4.板子上的LED灯引脚为PA1，与SPI_MISO引脚为同一个，不能再用LED表示通讯成功或失败
的状态。
5.通过USB转TTL模块连接PC与STK板,STK板与USB转TTL模块的连线方式如下；
@PrintfConfigStart
STK板        USB转TTL模块
PB4(TX)  -->  RX
PB5(RX)  -->  TX
GND      -->  GND
UART配置为波特率115200，数据位8，停止位1，校验位None
@PrintfConfigEnd

Notes:
1.You must first press the slave reset button to make the slave program run 
first,and then press the host user button to start running the host program, 
otherwise it will cause the master-slave communication failure.
2.The IO control mode can be set to interrupt mode and polling mode by the 
program in the master mode.
3.NSS pins only need to be connected when using the NSS hardware mode (this 
sample uses the NSS software mode, no need to connect the NSS pins)
4.The LED pin on the board is PA1, which is the same as the SPI_MISO pin, and 
can no longer use LEDs to indicate the status of communication success or 
failure.
5.Connect the PC to the STK board through the USB to TTL module, and the connection
method between the STK board and the USB to TTL module is as follows:
@PrintfConfigStart
STK board USB to TTL module
PB4(TX)  -->  RX
PB5(RX)  -->  TX
GND      -->  GND
UART is configured as BaudRate 115200, data bit 8, stop bit 1, and parity None.
@PrintfConfigEnd
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