查看“Arduino系列教程九：SPI”的源代码



Arduino开发板ICSP接口中MOSI, MISO,SCK为SPI接口，有的开发板D11,D12,D13管脚默认和SPI接口连接（如UNO PLUS）,有的开发板默认不连接。Accessory Shield开发板中OLED则是通过SPI接口控制。但本章教程作为Arduino的入门教程，OLED的程序较为复杂，在这里不打算讲解OLED的程序。在这里一Arduino IDE自带的例程讲解如何使用Arduino的SPI接口。
点击File->Examples->SPI->DigitalPotControl打开工程。程序如下：
<syntaxhighlight lang="python">
// inslude the SPI library:

#include <SPI.h>

 

// set pin 10 as the slave select for the digital pot:

const int slaveSelectPin = 10;

 

void setup() {

  // set the slaveSelectPin as an output:

  pinMode (slaveSelectPin, OUTPUT);

  // initialize SPI:

  SPI.begin();

}

 

void loop() {

  // go through the six channels of the digital pot:

  for (int channel = 0; channel < 6; channel++) {

    // change the resistance on this channel from min to max:

    for (int level = 0; level < 255; level++) {

      digitalPotWrite(channel, level);

      delay(10);

    }

    // wait a second at the top:

    delay(100);

    // change the resistance on this channel from max to min:

    for (int level = 0; level < 255; level++) {

      digitalPotWrite(channel, 255 - level);

      delay(10);

    }

  }

 

}

 

void digitalPotWrite(int address, int value) {

  // take the SS pin low to select the chip:

  digitalWrite(slaveSelectPin, LOW);

  //  send in the address and value via SPI:

  SPI.transfer(address);

  SPI.transfer(value);

  // take the SS pin high to de-select the chip:

  digitalWrite(slaveSelectPin, HIGH);

}</syntaxhighlight>
 

<b>程序分析：</b>
程序开始先引入SPI头文件SPI.h。SPI接口包含MOSI, MISO,SCK,CS四根线。其中MOSI, MISO,SCK已经固定引脚。而CS为片选引脚，可随意选择哪个引脚作为CS.程序中const int slaveSelectPin = 10;定义D10作为片选信号。
setup()函数中调用SPI.begin()初始化SPI接口。此处为默认设置。若要设置具体参数可使用如下语句初始化SPI.
<syntaxhighlight lang="python">
SPI.beginTransaction(SPISettings(14000000, MSBFIRST, SPI_MODE0));</syntaxhighlight>
SPISettings()函数设置SPI传输模式，SPI.beginTransaction()函数根据SPISettings()初始化SPI.
此处为设置SPI速率为14MHZ,高位先传输，模式0。
<syntaxhighlight lang="python">
digitalWrite(slaveSelectPin, LOW);</syntaxhighlight>
传输SPI前先拉低片选管脚，使能SPI设备。
<syntaxhighlight lang="python">
SPI.transfer(val)；</syntaxhighlight>
SPI传输函数，参数val为要发送的字节，函数返回值为接收到的数据。
<syntaxhighlight lang="python">
digitalWrite(slaveSelectPin, HIGH);</syntaxhighlight>
 

SPI传输结束释放片选管脚。