原理

I2C 分为两种模式共四个可能性，分别为

• Master Transmitter：主动发起 START，并向指定地址的 slave 传送数据，接受来自 slave 的 ACK，传输结束后主动发起 STOP
• Master Receiver：主动发起 START，并向指定地址的 slave 请求数据，向 slave 发送 ACK 并发起 STOP
• Slave Transmitter：接受来自 master 向本机地址发起的 START，向 master 传送数据，接受来自 master 的 ACK，并检测是否 STOP
• Slave Receiver：接受来自 master 向本机地址发起的 START，接受来自 master 的数据，向 master 发送 ACK，并检测是否 STOP

它们这样对应：
Master Transmitter <-> Slave Receiver
Master Receiver <-> Slave Transmitter

接线

两个 Arduino 之间进行 I2C 通信，接线如下

注意，因为 I2C 协议需要线与，所以要添加上拉电阻
这里选择 A4 和 A5 各 10k 上拉，如果需要更快的 I2C 通讯速度，可以降低电阻值

接线

加上 Probe

接线

代码

/** I2C_Master_Transmitter.ino
 * 
 * | Arduino | A4 | ---- SDA
 *           | A5 | ---- SCL
 */

#include <Wire.h>

void setup() {
  Serial.begin(115200);
  Wire.begin();       // join I2C bus as master (no address provided).
}

byte x = 0;

void loop() {
  uint8_t slave_addr = 0x02;
  Serial.println("Finish transmission");
  Wire.beginTransmission(slave_addr); // transmit to device
  Wire.write("x is ");        // sends five bytes
  Wire.write(x);              // sends one byte  
  Wire.endTransmission();    // stop transmitting

  x += 1;
  delay(100);
}

/** I2C_Master_Receiver.ino
 * 
 * | Arduino | A4 | ---- SDA
 *           | A5 | ---- SCL
 */

#include <Wire.h>

void setup() {
  Serial.begin(115200);
  Wire.begin();       // join I2C bus as master (no address provided).
}

void loop() {
  uint8_t slave_addr = 0x2;
  uint8_t n_bytes = 1;
  Wire.requestFrom(slave_addr, n_bytes);    // request data from slave device

  while (Wire.available() > 0) {  // slave may send less than requested
    char c = Wire.read();         // receive a byte as character
    Serial.print(c);
  }

  delay(100);
}

/** I2C_Slave_Transmitter.ino
 * 
 * | Arduino | A4 | ---- SDA
 *           | A5 | ---- SCL
 */

#include <Wire.h>

void setup() {
  uint8_t device_addr = 0x02;
  Serial.begin(115200);
  Wire.begin(device_addr);            // join I2C bus as slave (address provided)
  Wire.onRequest(requestEvent);       // register event
}

void loop() {
  delay(100);
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent() {
  Serial.println("replied");
  
  Wire.write("hello "); // respond with message of 6 bytes
  // as expected by master
}

/** I2C_Slave_Receiver.ino
 * 
 * | Arduino | A4 | ---- SDA
 *           | A5 | ---- SCL
 */

#include <Wire.h>

void setup() {
  uint8_t device_addr = 0x02;
  Serial.begin(115200);
  Wire.begin(device_addr);            // join I2C bus as slave (address provided)
  Wire.onReceive(receiveEvent);       // register event
}

void loop() {
  delay(100);
}

void receiveEvent(int howMany) {
  while(1 < Wire.available()) {
    char c = Wire.read(); // receive byte as a character
    Serial.print(c);
  }
  int x = Wire.read();    // receive byte as an integer
  Serial.println(x);
}

示波器图形

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